Protein&coherence 2

Papers, articles etc. relevant to quantum coherence and entanglement in protein, including Ishizaki & Fleming and Satinover.

1.) re: high temperature quantum coherence in biological matter:
Coherently wired light-harvesting in photosynthetic marine algae at room temperatures

2.) Brain coherence and entanglement in the 21st century

3.) Theoretical examination of quantum coherence in a photosynthetic system at physiological temperature - Ishizaki & Fleming - Extends from earlier studies to investigate quantum coherence in protein at physiological temperatures.

4.) The Quantum Brain - Jeffrey Satinover - Interesting for its discussion of quantum activity in protein

1.)

ROOM TEMPERATURE QUANTUM COHERENCE IN PROTEIN

Coherently wired light-harvesting in photosynthetic marine algae at ambient temperatures

Elisabetta Collini, Cathy Wong, Krystyna Wilk, Paul Curmi, Paul Brumer & Gregory Scholes

Universities of Toronto, New South Wales and Padua

Nature, 463, pp. 644-7, 4 February 2010 doi:10.1038/nature08811

INTRODUCTION: This low-key paper may in time come to be seen as one of the decisive studies of the 21st century. The paper shows that room temperature quantum coherence can occur in biological matter. In 2007, Engel et al had shown that coherence was possible in organic matter, but this was only demonstrated at very low temperatures, whereas the Collini study demonstrates similar activity at ambient temperature. The paper and related commentaries makes no mention of consciousness, although a relevance to quantum computing is suggested, which is a possible step towards discussing consciousness. The main plank of the arguments against quantum consciousness relates to the speed of decoherence in biological matter being too quick for coherence to be relevant to processing, particularly neural processing, in such matter. This argument looks to have been substantially undermined by the recent study.

Antenna proteins are an essential part of the photosyntetic process, which absorbs light and transmits the resulting excitation between molecules to a reaction centre. Recent research has concentrated on determining the mechanisms that support a very high level of efficiency in this energy transport. Light-harvesting antennas are comprised of eight pigment-molecules, with different pigments absorbing different frequencies of light. The route the energy takes across the molecule is important in terms of energy efficiency.

Studies have documented the fact that light-absorbing molecules in some photosynthetic proteins transfer energy according to quantum mechanical rather than classical laws even at ambient temperature. This contradicts the 20th century dogma that long-range quantum coherence would always decohere in the temperatures found found in biological systems.

This paper by Collini et al describes X-ray crystallography studies of two types of marine cryptophyte algae that have long-lasting excitation oscillations and correlations and anti-correlations, symptomatic of quantum coherence even at ambient temperature. Distant molecules within the photosynthetic protein are thought to be connected to quantum coherence, and to produce efficient light-harvesting as a result. The cryptophytes can photosynthesise in low-light conditions suggesting a particularly efficient transfer of energy within protein. According to the traditional theory, this would imply only small separation between chromophores, whereas the actual separation is unusually large.

In this study, performed at room temperature, the antenna protein received a laser pulse, which results in a coherent superposition in the protein. The experimental data of the study shows that the superposition persists for 400 femtoseconds and over a distance of 2.5 nanometres. Quantum coherence occurs in a complex mix of quantum interference between electronic resonances, and decoherence caused by interaction with the environment. The authors think that long-lived quantum coherence facilitates efficient energy transfer across protein units.

The authors remains uncertain, as to how quantum coherence can persist for hundreds of femtoseconds in biological matter. One suggestion is that the expected rate of decoherence is slowed by shared or correlated motions in the surrounding environment. Where light-harvesting chromophores are covalently bound to the protein backbone, it is suggested that this may strengthen correlated motions between the chromophores and the protein.

In the same issue of 'Nature' that published Collinis study, the 'News and Views' section of the journal also comments on her paper. It emphasises that this is the first study in which quantum coherence in photosynthetic proteins has been observed at room temperature. It comments on the remarkable efficiency of energy transfer, between the antennas that guide excitation energy from hundreds of light-absorbing pigment molecules towards the subsequent reaction centres that drive biochemical events. Collini is suggesting that quantum coherence could be a factor in this efficiency.

Earlier studies had observed coherent behaviour in green sulphur bacteria, but at very low temperatures. Collini et al observed quantum coherence in the antenna, and found that this persisted over 400 femtoseconds, in contrast to an expectation in traditional theory of only 100 femtoseconds. Coherence was observed between widely separated pigment molecules. This has also been observed in bacterial light-harvesting complexes. However, this was at very low temperatures, while the Collini study was at room temperature. Engel et al, who were responsible for some of the earlier studies, have speculated that quantum coherence allows antennas to search for the lowest energy state of the complex more efficiently, thus enhancing the energy transfer to the reaction centre. Coherence might help excitations to avoid local energy traps or minima, on their way to the reaction centre. Covalent binding to the protein backbone is speculated to make coherence longer lasting.

Perhaps the most surprising aspect of this latest paper on coherence in proteins is the speed with which news of the development has made its way to the level of more popular science, in the form of a useful full page summary by Kate McAlpine in the 'New Scientist'. She mentions that Gregory Engel, who was respnsible for the earlier low temperature studies of coherence in bacterial proteins, is enthusiastic about the Collini result. Engel and his group have also performed a study at 4 degrees centigrade, much above previous levels, although below the 21 degrees of the Collini study. Engel is also quoted as saying that this work could have implications for quantum computing, where a core problem has been to operate at the very low temperatures that are usually thought necessary to prevent quantum decoherence. The speed with which this work has been picked up and given prominence in a popular science magazine suggests a background change of attitude to coherence in protein. The vexed question of quantum consciousness is not mentioned, but the suggestion of activities within protein as a model for quantum computing is moving is in that direction.

2.)

Brain coherence and entanglement in the 21st century

Derived from various sources referenced below

The debate over quantum coherence and entanglement in the brain and their possible connection to consciousness may have been moved into a new stage by the discovery that quantum coherence has a functional role in the transfer of energy within proteins, the basic building blocks of living cells (1. Engel et al, 2007). Most importantly, it knocks a hole in the central argument against quantum consciousness, which has been the claimed impossibility of quantum coherence being sustained for any useful period in biological matter. At the same time, it moves the discussion of what sort of coherent features could support consciousness on from a phase of pure theorising, to a phase in which ideas can be related to features that have been shown to exist in biological matter.

In the nearly three years since Engel's study was published in Nature, there has been almost no discussion of the possible significance of this finding in relation to consciousness. Anyone familiar with mainstream consciousness studies in the last ten years, where the very mention of quantum consciousness produces a braying chorus of 'fringe' and 'pseudoscience', will not be surprised by the absence of constructive comment from that direction. Engel and other researchers in the field of quantum coherence in protein are not involved in researching consciousness, and would probably not improve their chances of funding, if they suggested there was any connection to consciousness. More disappointing is the relative lack of discussion within the very limited realm of quantum consciousness studies.

Hameroff has referred to Engel et al as evidence for quantum coherence in the brain, but does not appear to have discussed the large difference between the time to collapse in Engel's study and the much longer time in the Orch OR model. Georgiev (2. ) criticises Hameroff's model for not being synchronised with the 10-15 picosecond (picosecond=10^-12 seconds) timescale, which governs much of the activity in protein and enzymes, but again does not really engage with the Engel study.

I am reluctant to cross the line from merely commenting on studies, to making more or less original comments, but confronted with an effective research vacuum, I feel forced to do this to a limited degree. Hameroff, and Georgiev at least sometimes, relate to models based on Penrose's idea of objective reduction (OR), in which the self-collapse of quanta that have not interacted with the environment gives access to understanding or consciousness as a fundamental property of spacetime. In this model, the important question is whether this objective collapse or reduction occurs within a timescale that could be relevant to neural processing. A single quanta in isolation might not decohere for millions of years. Some more substantial quantum system is needed to make this model of quantum consciousness plausible. This is where the possibility of the entanglement of many quanta, giving a larger, more energetic, quantum feature, and thus a longer time to reduction that is more in line with neural processes becomes interesting.

Engel et al studied photosynthesis in green sulphur bacteria. Unpromising as this may sound, much the same principles apply across all multicellular living tissues, and this means that the nature of processing in these complexes could be relevant to what happens in neurons. The photosynthetic complexes (chromophores) in the bacteria are tuned to capturing light and transmitting its energy to long-term storage areas. It should be stressed that in this system, photons (the light quanta) only provide the initial excitation, and the coherence and entanglement discussed here involves electrons in the protein.

It is the energy transfer mechanism that is of interest in this case. Traditionally, this had been analysed in terms of classical physics. However, the Engel study documented the dependence of the energy transport on the spatially extended properties of the wave function of the photosynthetic complexes. In particular, the timescale of the quantum coherence observed was much longer than would normally be predicted for a protein environment, with a duration of at least 660 femtoseconds (femtosecond=10^-15), nearly three times as long as the normally predicted times of 250 femtoseconds. In the latter case, rapid destruction of coherence would prevent it from influencing the system.

Engel does not offer much discussion of the reason for this delay in decoherence, but it could be crucial if this process is related to quantum consciousness. This particular feature should be a wake up call for students of quantum consciousness, since almost the only rational debate in this area has centred on whether the time to quantum decoherence in living matter could be long enough for it to be relevant to neural processes. The delay from 250 to 660 femtoseconds hints at some kind of protection or screening of coherence, analogous to the screening argued for by Hameroff.

Engel further points out that there is a considerable adaptive advantage to using quantum coherence, in that it allows the photosynthetic complexes to sample a vast number of different routes, in order to find the most efficient one. Engel views the system as performing a single quantum computation, sensing many states simultaneously and selecting the correct answer. This process is analogous to Grover's algorithm. The involvement of quantum coherence explains the extreme efficiency of the system. Engel also considers the possibility that non-local entanglement is involved in the quantum activity within the chromophores. Some earlier models had recognised coherence between donor and acceptor electrons, but Engel says that to account for the unexpectedly long-lived coherence it is necessary to accept that protein has an active role in the coherence. Towards the end of his paper, Engel stresses that his findings may have further implications in that protein may itself produce the structures that in turn give rise to further coherence transfer.

Other recent studies give support to Engel's work. Collini & Scholes (3. 2009) view the chromophores as a situation in which protein can protect coherence from the environment. In a paper by Fleming and co-workers (4. 2007) that relates to the earlier work by Engel, the authors look at evidence that a collective long-range electrostatic response of protein to electronic excitation is responsible for sustained quantum coherence. The protein environment both protects coherence, and increases the efficiency of energy transport.

In a 2009 paper, Sarovar et al (5.) examined the subject of possible quantum entanglement in the photosynthetic complexes discussed above. Entanglement carries the possibility of a large number of particles acting as a single quantum feature, and having a time to objective reduction that could have some bearing on neural processing. The paper starts from the base of quantum coherence between the spatially separated chromophore molecules found in these systems. The entanglement examined is the non-local correlation between the electronic states of spatially separated chromophores. Coherence is a necessary and sufficient state for entanglement to exist. The coherence properties of the photosynthetic complex reflect the interplay of the protein with the decoherence effects of the environment.

Ishizaki and Fleming (2009) developed an equation that allows modelling of this system. Where this deals with the initial sites to be excited by the light energy, the initial entanglement rapidly decreases to zero, but then increases again after about 600 femtoseconds. This is thought to be a function of the entanglement of the initial sites being transported and localised at other sites, but remaining coherent at these other sites, from which further entanglement can subsequently resurge. Interestingly, the timescale of entanglement between the different sites in the photosynthetic complex is much longer than for coherence. The coherence is 660 femtoseconds or greater, while entanglement can last for about 5 picoseconds at the relatively low temperature of 77 Kelvin or 2 picoseconds at room temperature. The authors regard this as remarkable in the conditions of biological matter. This study is only the result of modelling, but is considered to be experimentally verifiable. The few picosecond timescale for entanglement suggested in Sarovar's paper is any case getting into something like the same ballpark as the 10-15 picoseconds relevant to much protein and enzyme activity. Other studies appear to confirm the existence of picosecond timescales for entanglement in chromophores. It is not clear to the authors that entanglement is actually functional in chromophores. Coherence appears to be sufficient for very efficient transport of energy, and entanglement may be only a by-product of coherence. At the same time, it is speculated that such entanglement might provide a lead in the development of quantum technologies.

Also in a 2008 paper (7.), Cia et al looked at the possibility of quantum entanglement in the type of system studied in the Engel paper. Cia takes the view that entanglement can exist in hot biological environments. The paper draws attention both to a paper in Nature demonstrating quantum tunnelling by enzymes (8. Ball, 2004), and to the Engel paper referred to above. Biologists have been generally sceptical as to the possibility of quantum entanglement in living matter. However, Cia says that such thinking is based on the assumption of thermal equilibrium, whereas biological systems are far from thermal equilibrium. Cia points out the conformation of protein involves interactions at the quantum level. These are usually treated classically, but Cia wonders whether a proper understanding of protein dynamics does not require quantum mechanics. It is said not to be clear, whether or not entanglement is generated during the motions of protein, but that entanglement might have important implications for the functioning of protein.

The model studied by the Cia et al paper suggests that while a noisy environment, such as that found in biological matter, can destroy entanglement, it can also set up fresh entanglement. It is argued that entanglement can recur in the case of an oscillating molecule, in a way that would not be possible in the absence of this oscillation. The molecule has to oscillate at a certain rate relative to the environment to become entangled. This allows for entanglement to emerge, but this would normally also disappear quickly. Something extra is needed for entanglement to recur or persist. It is suggested that the environment, which is normally viewed as the source of decoherence, can play a constructive role in resetting entanglement, when combined with classical molecules. Environmental noise in combination with molecular motion provides a reset mechanism for entanglement. The suggestion that entanglement can exist by resetting itself in a noisy environment, and the further suggestion of possible entanglement in Engel's photosynthetic structures point to the possibility that relatively large structures are entangled, with times to objective reduction that could be relevant to neural activities.

Following the recent papers discussed above, the debate on quantum coherence in living tissues has moved to a new stage. We now have definite evidence of functional quantum coherence in living matter, and also modelling that makes it likely that there is also quantum entanglement in living matter. In looking for a possible mechanism for quantum consciousness, the principle of Occam's razor suggests that that we should work with existing evidence, rather than more speculative possibilities. In the present state of knowledge, the findings with photosynthetic protein appear to be a more promising basis than either the very ambitious timescales of the Hameroff model, which put heavy demands on the possible amount of microtubule screening, or the less ambitious timescales suggested by Jibu and Yasue for quantum brain dynamics, which, however, relate to the water dipoles in a way not immediately seen to be relevant to the actually demonstrated coherence/entanglement in photosynthetic complexes. The structures described do not immediately provide a linking mechanism to the various timescales to which theorists have attempted to link coherence or entanglement in the brain, but it is not possible to match all these features, which have included Libet's half second, the gamma synchrony and the processing timescales of proteins and enzymes. The studies discussed above suggest there is an existing means by which quantum consciousness might be supported in the brain. It is possible that once established there quantum consciousness can influence other features such as the gamma synchrony by further intermediate steps. There appears to be a good argument for concentrating the attention of such study that is given to quantum consciousness in this area.

References:-
1.) Engel et al (2007) - Evidence for wavelike energy transfer through quantum coherence in photosynthetic systems - Nature, 446, pp. 782-6 doi:10.1038
2.) Georgiev, D. (2004) - Bose-Einstein condensation of tunnelling photons in the brain cortex as a mechanism of conscious action
3.) Collini, Elisabetta & Scholes, G. (2009) - Coherent intrachain energy in migration in a conjugated polymer at room temperature - Science, vol. 323 No. 5912 pp. 369-73, DOI: 10.1126
4.) Lee, H., Cheng, Y. & Fleming, G. (2007) - Coherence dynamics in photosynthesis: Protein protection of excitonic coherence - Science, 316, 1462
5.) Sarovar, M. et al - Quantum entanglement in photosynthetic light harvesting complexes
6.) Ishizaki, A. & Fleming, G. (2009) - On the adequacy of the Redfield equation and related approaches to the study of quantum dynamics in electronic energy transfer - Journal of Chemical Physics
7.) Cia, J. et al, (2009) - Dynamic entanglement in oscillating molecules - arXiv:0809.4906v1 [quant-ph]
8.) Ball, (2004) - Nature, 431, p. 792

3.)

Theoretical examination of quantum coherence in a photosynthetic system at physiological temperature

Akihito Ishizaki & Graham Fleming

University of California, Berkeley & Lawrence Berkeley National Laboratory

PNAS, 7 August 2009

INTRODUCTION: Relative to the study of quantum coherence in photosynthetic protein, this paper builds on the earlier work of Engel et al in looking at the question of quantum coherence at physiological temperatures. The authors' investigation indicates that coherence may be sustained for a significant length of time at these temperatures, and possibly almost as long as at the cyrogenic temperatures used in the Engel study.

This paper builds on the work of Engel et al (2007) [1.] in studying quantum coherence in photosynthetic proteins. The purpose of the paper is to study the action of quantum coherence at the physiological temperature of 300 Kelvin, rather than the cryogenic temperature of 77 Kelvin use in the Engel study. Theoretical investigation in this paper reveals that quantum wavelike motion can also persist at physiological temperatures. It is suggested that this may be involved in the transfer of energy from the light-harvesting antenna to the reaction centre complex in photosynthetic proteins. Quantum coherence may serve to overcome local energy traps, and thus aid the efficient trapping of electronic energy by the pigments.

This study refers to the Fenna-Matthews-Olson (FMO) pigment-protein complex found in low light-adapted green sulphur bacteria. The FMO is situated between the chlorosome antenna and the reaction centre, and its function is to transport energy harvested from sunlight by the antenna to the reaction centre. The FMO complex is a trimer of identical sub-units, each comprised of seven bacteriochlorphyl (BChl) molecules. This structure has been extensively studied. Quantum coherence in the structure has been assumed to decohere too rapidly to be relevant to its function, until the Engel et al study in 2007. In the Engel et al study, the observed coherence lasts for a similar timespan to the excitation energy transfer (EET). This implied that the excitation energy transfer passed through the FMO complex by means of quantum coherence, rather than by involving a classical process. Long-lasting quantum coherence has also been observed in purple bacteria (2. Lee et al, 2007). It is suggested that quantum coherence is responsible for the remarkably high efficiency of EET transfer in photosynthetic bacteria.

However, the Engel and Lee studies were performed at low temperatures, whereas quantum coherence becomes more fragile at higher temperatures, because of the higher amplitude of environmental fluctuations. In this paper, the equation supplied by the authors suggest that coherence could persist for several hundred femtoseconds even at physiological temperatures of 300 Kelvin. EET dynamics are considered within one sub-unit of the FMO, as inter sub-unit coherence would be expected to be too rapidly destroyed by the environment, to be relevant to energy transfer. Each unit comproses 7 BChl molecules. BChl 1 and 6 are orientated towards the chlorosome antenna, and are the initially excited pigment, and BChl 3 and 4 are orientated towards the reaction centre. Even at the physiological temperatures, quantum coherence can be observed for up to 350 femtoseconds in this structure. This suggests that long-lived electronic coherence is sustained among the BChls, even at physiological temperatures, and may play a role in the high efficiency of EET in photosynthetic proteins.

BChl 1 and 6 are seen as capturing and conveying onward the initial electronic energy excitation. Quantum coherence is suggested to allow rapid sampling of pathways to BChl 3 that connects to the reaction centre. If the process was entirely classical, trapping of energy in subsidiary minima would be inevitable, whereas quantum delocalisation can avoid such traps, and aid the capture of excitation by pigments BChl 3 and 4. BChl 6 is strongly coupled to BChl 5 and 7, which are in turn stongly coupled to BChl 4, ensuring transfer of excitation energy. Delocalisation of energy over several of the molecules allows exploration of the lowest energy site in BChl 3.

The study predicts that qauntum coherence could be sustained for 350 femtoseconds, but if the calculation is adjusted for a possible longer phonon relaxation time, this could extend to 550 femtoseconds, still at physiological temperatures. A study be Collini & Scholes (3. 2009) supports the idea of long lived quantum coherence at room temperature.

References:-
1.) Engel et al, (20070 - Evidence for wavelike energy transfer through quantum coherence in photosynthetic systems - Nature, 446, pp. 782-6
2.) Lee et al, (2007) - Coherence dynamics in photosynthesis: Protein protection of excitonic coherence - Science, vol. 316
3.) Elizabetti Collini & Gregory Scholes, (2009) - Coherent intrachain energy migration in a conjugated polymer at room temperature - Science, vol. 323, no. 3912, pp. 369-73, DOI: 10.1126/science. 1164016

4.)

The Quantum Brain

Jeffrey Satinover

John Wiley & Sons (2001)

INTRODUCTION: This book is mainly of interest for its discussion of quantum features and particularly quantum tunnelling in protein, an area which more mainstream science popularisations are not often keen to discuss. Since Satinover wrote this book, the discovery of functional room-temperature, quantum coherence in photosynthetic protein has brought the importance of quantum activity in protein more to the fore. Apart from this discussion about protein, Satinover is mainly interested in developing the idea of quantum ramdomness driving chaos-based patterns of macroscopic neural processing. Although, he appears to derive a good part of his material from Penrose and Hameroff, he is more concerned with information processing than consciousness, and chooses to dismiss the Penrose/Hameroff consciousness theory without a proper discussion of the matter.

The researcher, John Hopfield, demonstrated that a type of neural net, now known as a Hopfield network, has an identical mathematical description to magnetic systems called spin glasses. These are magnetic substances that demonstrate collective behaviour, without the need for external orchestration.

Satinover discusses a stable arrangement of magnets, in which opposite poles are holding the magnets apart. If the system is vigorously disturbed, this stable arrangement breaks down, but after a time, the system will settle into a new stable arrangement, to which it can always return after minor disturbances, although now there are more magnets than previously that are not aligned in parallel.

Ferromagnetic materials such as iron have many small areas or domains, in which electron spins (effectively magnetic charges) are aligned. But the domains have many different alignments, and these electrons are in a precarious position, where they can easily be flipped into a new alignment.

These ferromagnetic groups of neighbouring spins are mathematically similar to the excitatory (mainly glutamate) connections between neurons. However, in addition to spins that try to align in the same direction, there are antiferromagnetic systems that align in alternate directions, and these turn out to be mathematically similar to the inhibitory (mainly GABA) connections between neurons.

Materials that have ferromagnetic and antiferromagnetic domains mixed are referred to as spin glasses. This is a random mix of ferromagnetic and antiferromagnetic material, where adjacent electrons competing to align, or flip one another, are always on the edge of change, and are argued to resemble the analogous excitatory and inhibitory mix of neurons. A spin glass system has more than one 'best arrangement' and is similar to a brain, in that it can store new data without erasing existing material.

The brain and chaos: The brain is here regarded as a self-organising system that mathematically resembles the spin glass structure discussed above. However, it is pointed out that self-governing ensembles have a tendency towards chaos, meaning not actual disorder but deterministic chaos. The development of the system could in principle be described by an algorithm, but because this would require such a vast amount of information, the system is in practice unpredictable. The system does repeat patterns or behaviour, but they are similar, rather than exactly the same. It is suggested here that quantum randomness in areas of the brain might be amplified by chaos.

Microtubules: Satinover is interested in the possible involvement of microtubules in brain processing. The cytoskeleton, of which microtubules are the most important component, is considered to be uniquely suited to carry signals, because it spans the whole cell. The cytoskeleton used to be viewed, mainly as a support structure, but more recent studies (1&2) show that they are also signalling mechanisms. The self-organised activity of microtubules and associated proteins and filaments, is seen in recent visualisation studies, to control the mobility of cells and the configuration of dendrites, through which signals enter the cell. This structure is likened to the update rules governing interaction between neighbouring units which drives the evolution of so-called cellular automata from simplicity to complexity. Within the hexagonal tubulin grid that makes up the microtubule, each tubulin has six immediate neighbours, an arrangement of the same type as those conjectured by cellular automatons. The microtubule network as a whole is said to be harmonious and suitable for the transmission of vibrations. It is suggested that the neuron network of the brain is linked to the internal microtubule processing within neurons. The microtubule network is viewed as analagous to the Hopfield network and spin glass systems discussed above.

Quantum aspects of protein: The best section of this book is the discussion of the quantum aspects of protein, the basic building blocks of organic matter. A protein is a string of a hundred or more amino acid molecules. The amino acids are attached to one another by bridges called peptides, so that the protein is a macromolecule. Each amino acid has a unique shape, and a unique distribution of electric charge. For a protein to carry out its necessary functions within an organism, it must fold in a precise manner, at or very close to, the energy minima.

The problem with this system is that there can be trillions of similar ways for a protein to fold. Proteins can assume a very large number of conformational states, with a large number of energy minima. Despite this huge number of possible states, proteins can, within seconds, find the correct conformations and energy minima, which are also the most functional configurations.

There is, as yet, no clear indication as to how this is to be achieved. Random searching for a minimum energy conformation would take longer than the life of the universe to reach a solution. The position is not much better for supercomputers, where despite years of generous funding, it has proved impossible to calculate the minimum energy configuration for even a short chain of amino acids. This is known as the protein-folding problem. DNA encodes the primary structure of the protein, which is the sequence of the amino acids. At a secondary stage, the amino acid chains are formed into particular shapes, such as helices. At the tertiary stage, sections of helices and other shapes are brought together, and folded into a particular configuration of electric charges. It is this last stage of folding that constitutes the protein-folding problem. Satinover argues that the problem of protein folding is similar to the means, by which spin glasses reach alignment, with a huge number of axes, along which protein must flip.

Satinover explains that to achieve what they do proteins use quantum features. Some of the electrons in the protein are in a wave or superposed state, with the wave extending over a considerable distance through the protein. This is referred to as tunnelling, with the wave form of the electron able to penetrate into regions that the point-particle form of the electron cannot reach. This electron tunnelling can be exceptionally sensitive to minor couplings. In helical structures in particular, the influence of quantum tunnelling falls off only slowly with distance. The tunnelling of electrons triggers conformational changes in protein, and further to this, conformational changes in protein trigger yet more quantum tunnelling. Water is vital to living organisms, and it also exhibits tunnelling between molecules. The tunnelling process orders water into chiral (left and right-handed) clusters, which play an important role in protein folding. Tunnelling makes low-energy states more accessible within protein, and this probably proved to be an adaptive advantage, from an early stage in evolution. Studies by Peter Wolynes at the Centre of Biophysics and Computational Biology and also at the National Centre for Supercomputing Applications have simulated the tunnelling process in protein, showing that theories of spin glasses can be applied to the protein-folding problem, and also showing that tunnelling makes systems more efficient, particularly in the search for minimum energy levels. The advantage of quantum processing is that an electron can simultaneously search many routes for the most efficient route.

The existence of quantum tunnelling in protein raises the question of the vulnerability of quantum processes to decoherence. In general, the movement of molecules as a function of heat serves to disrupt quantum tunnelling. However, it is claimed that the opposite is true in the case of protein. Proteins also exhibit phonons that represent travelling, classical, mechanical coherence in protein. These are claimed to enhance tunnelling distance. This represents a mutually reinforcing relationship between classical, mechanical vibrations and quantum activity, so as to enhance short-lived coherences. Decoherence of superpositions may happen rapidly, but may collapse to just the right classical state, which also puts the protein into the right condition for the next burst of quantum coherence. Studies performed a number of years after Satinover's book look to have demonstrated just such a pattern of decline and resurgence in coherence, where quantum coherence has been demonstrated in photosynthetic proteins.

Tunnelling by hydrogen protons has been found to be essential for enzymatic action. Here again, there is an interaction between tunnelling protein conformation and more tunnelling, and here too, studies show that classical vibrations, rather than disrupting tunnelling, are actually required for tunnelling. Thus proteins, merely be absorbing heat from the environment, can initiate computational processing. Life here seems to use quantum effects to extract order from disorder. A study by Judith Klinman (3.) at Berkeley showed that hydrogen proton tunnelling in protons can occur at room temperature.

Subsequent to its discussion of quantum effects in protein, this book becomes less interesting. Ultimately, it is commited to 'the brain's a deterministic computer doctrine', albeit a computer driven by quantum randomness feeding into deterministic chaos. In essence the writer is concerned with quantum/chaotic information processing rather than consciousness.

Satinover appears to derive quite a lot from Penrose and Hameroff, but as is often the case, intellectual rigour goes out of the window, when discussing this theory. The whole theory appears to be dismissed solely on the basis of the Hameroff side of the theory, which is to do with implementation in the brain, rather than Penrose's original reasons for looking to quantum theory. Furthermore, if one is to argue against this theory on the basis of decoherence, as happens here, it is necessary to discuss the possibility of shielding of quantum processes, or the possible involvement in consciousness of the shorter lived coherences discussed by Satinover. This discussion is lacking in this book.

References:-
1.) Tuszynski, J. et al (1998) - Information processing and quantum computation in microtubules - Philosophical Transactions of the Royal Society 2.) Brown, J. & Tuszynski, J. (1997) - Dipole interactions in axonal microtubules as a mechanism of signal perception - Physical Review E 56, pp. 5834-40
3.) Bahnson, B. & Klinman, J. (1995) - Hydrogen Tunnelling in Enzymes Catalysis - Methods in Enzymology, 249, pp. 373-397
4.) Wolynes, P. (1992) - Spin glass ideas and the protein folding problem - In: Spin Glasses and Biology, pp. 225-6 - Ed. Stein, D. - World Scientific Publishing
5.) Farid, R. et al (1993) - Electron transfer in proteins - Current Opinion in Structural Biology, 3, p.225
6.) Stuchebrukov, A. (1996) - Tunnelling currents in electron transfer reactions in proteins - Journal of Chemical Physics, 105, pp. 10819-10829
7.) Balabin, I. & Onuchic, J. (1998) - A new framework for electron transfer calculation - Journal of Physical Chemical B, 102, pp. 7497-7596
8.) Ogawa, M. et al (1993) - Distance dependence of intramolecular electron transfer rates across oligoprolines - Journal of Physical Chemistry, 97, pp. 11456-11463
9.) Balabin, I. & Onuchic, J. (1996) - Connection between simple models and quantum mechanical models for electron transfer tunnelling - Journal of Physical Chemistry, 100, pp. 11573-11580
10.) Basran, J., Sutcliffe, J. & Scrutton, N. (1999) - Enzymatic H-transfers requires vibration driven exteme tunnelling - Biochemistry, 38, pp. 3218-3222
11.) Wolynes, P. & Kuki, A. - Electron transfer paths in protein - National Center for Supercomputing Applications