I-SIS Book Review
Dr. Mae-Wan Ho reviews Life at the Cell and Below-Cell Level: The Hidden History of a Fundamental Revolution in Biology
by Gilbert N. Ling, Pacific Press, New York, 2001 ISBN: 0-9707322-0-1
On the face of it, cell biology is booming. Advances in laser optics and multi-photon techniques are producing ever brighter and sharper pictures of cells, even live ones. Fluorescent labels make it possible to find out which regions of the genome are transcribed when; and to track any and every protein in action within the cell.
These images are living chronicle of the astonishing diversity of molecular species that the cell uses in signal transduction and downstream processes; the multitude of genes and non-gene regions of the genome transcribed, the coding messages translated into protein and transported to the organelles to transform material and energy, to remodel the cells cytoskeleton, to power arrays of molecular motors, not to mention the battalions of molecular pumps in the cell membrane that must be energized to keep out unwanted ions and metabolites, the receptors and gates that must be flipped open to let the nutrients in through special channels and to discharge secretions and wastes to the outside. And all that molecular hardware the cell churns up and replaces with unseemly haste and extravagance as it goes about its business of living.
It simply defies the imagination to figure out how the cell can keep changing shape and substance yet maintain its unmistakable identity, or else, even more mysteriously, manage to switch identity to become a different kind of cell. And above all, no matter what it does, a cell never loses its sense of being an organising, organized whole.
There is a dearth of new ideas that can lift cell biology out of the pervasive molecular malaise that has infected all of the life sciences to varying degrees in this post-genomics era: a proliferation of molecular hardware and data, with no modicum of general understanding on the horizon.
Strong medicine is needed; and I have no hesitation in recommending Gilbert Lings latest book. But, like any strong medicine, it is not for the faint-hearted. I only took it after plenty of encouragement, which is what I hope to pass on to you.
I met Ling for the first time at the prestigious Gordon Research Conference on Interfacial Water in Cell Biology in Mount Holyoke (Bradley, Massachusetts, USA) in June 2004. He gave one of the two keynote lectures the first evening, and speaker after speaker referred to him throughout the week. He was the undisputed hero of the day. It was his moment of triumph after half a century of relative obscurity. Everyone, including me, cheered silently for him, and wished him well with all our heart, as though our own destiny and repute depended on it.
Ling was the hero among a select bunch of fiercely independent and original scientists in the true sense of the word, motivated by the quest for knowledge of nature above all else, setting aside personal prestige, politics, worldly success; often at great personal sacrifice and hardship. Many of the scientists, like Gilbert Ling, have not been afraid to ask big questions, such as posed by the celebrated quantum physicist Erwin Schrödinger sixty years ago: "What is life?" It is indeed a mistake to call such scientists mavericks and dissenters, because there is nothing arbitrary about their refusal to accept the conventional theory thats riddled with holes and falsehoods; and no coincidence that they are converging on a more accurate view of what life is.
Lings thesis is so important, and so original, that his books should have been read and understood by everyone at least ten, if not twenty years ago. Sadly, to answer the big question he is after, or to recognize the answer, requires an understanding of both physical and biological sciences to a degree thats beyond most scientists. I know, because I had tried to read an earlier book of his 20 years ago, before I was quite ready, and failed almost completely to comprehend it.
This time round, I was determined to discover for myself what it was that had inspired so many other scientists at the Gordon Conference; and I was thrilled to get an autographed copy of the latest book from the author himself.
Yet, I had to put the book down five times before finishing it some three months after I began. Ling has made even his latest book unnecessarily difficult by reproducing innumerable graphs from his scientific papers, often shrunk down to the point of illegibility and heavily annotated with small print besides.
The subtitle "The Hidden History of a Fundamental Revolution in Biology" may explain why Ling has gone to such lengths to document his own work and the contribution of others with abundant notes and references (557 in all), which also chopped up the text and spoiled the flow. My advice therefore is to get on with the text, ignoring both the graphs and notes, only checking them if you feel you must. You will be rewarded towards the end, as I was.
In case you are wondering about Lings credentials, he and Chinese physicist C.N. Yang were co-winners of the Chinese national Boxer fellowship that enabled them both to go to study in the United States. Yang won the Nobel Prize in Physics in 1957, while Ling soon found himself at odds with the most fundamental theory in cell biology: that the cell membrane is what keeps the cell intact, by pumping sodium out in exchange for potassium - which is why the cell has a high concentration of potassium and low concentration of sodium, precisely the opposite of the fluid outside - and acting as gate-keeper for glucose and other metabolites, not to mention numerous receptors in the membrane that are involved in signal transduction.
Armed with a thorough knowledge of physical chemistry and statistical mechanics, Ling proceeded to debunk the conventional membrane theory with meticulous experiments, based on which he developed several theories that fit the observations much better than the cell membrane theory.
For example, cut muscle cells with big holes in their cell membrane nevertheless excluded sodium in favour of potassium; furthermore, the cell would need up to 30 times the ATP it has just to pump out the sodium, leaving nothing for other activities.
Lings theories explain the most basic biology of the cell in terms of the physicochemical state of the protoplasm, the matrix of the living cell. I shall try to sketch the bare outlines to help orientate readers who will find much, much more in the book itself.
The first idea to grasp is that the 70% or so by weight of water associated with the cell - cell water - is not like water in bulk (even though thats mysterious enough, see SiS 23). Instead, the water molecules are aligned in ordered layers over a matrix of extended proteins in the protoplasm (see Fig. 1).
Figure one. The multiple layers of water molecules aligned over a hydrophilic surface.
Most people nowadays accept that water molecules immediately next to the hydrophilic (water loving) surface of proteins are bound in some way to the surface, so their motion is much more restricted than it would be in bulk water, but few believe this applies to more than one to several layers of water molecules. Ling, however, believes that practically all the cell water is restricted in motion and arranged in polarized multilayers.
This organised water has unusual properties, among which, its ability to partially exclude molecules and ions with large hydration shells, which include the sodium ion, Na+. That is essentially why the cytoplasm, even without its cell membrane will bind the smaller potassium ion, K+ in preference to Na+, and the latter need not be pumped out of the cell by an energy consuming mechanism.
In fact, the bulk of potassium does not exist in free solution in the cytoplasmic matrix. It is associated with fixed negative charges on the carboxylic acid side chains of the proteins. That is the earliest of Lings theories, which explains why K+ is not freely diffusible even in a muscle cell that lacks an intact cell membrane, and externally applied Na+ is still excluded from the cell.
In an astonishing, apparent confirmation of Lings polarized multilayers or PM hypothesis, Gerald Pollack and colleagues in Washington University, Seattle, USA, used a suspension of 0.5 to 2 micron diameter microspheres that can be seen under the microscope, and showed up massive exclusion zones clear of all or almost all microspheres extending millions of layers of water molecules from the hydrophilic surfaces of gels (see SiS 23). Perhaps other explanations are possible, but they are not yet convincing. Pollack was inspired by Ling to write a highly readable book that I have reviewed previously (see "Biology of least action", SiS 18).
A confirmation of Lings fixed charge hypothesis - that K+ is associated with carboxylic acid side chains predominantly in the myosin-rich bands in muscle - came from the work of Ludwig Edelmann of Saarland University in Germany, who was also at the Gordon Conference (see "What is the cell really like?" this issue).
But still, a major difficulty for conventional biochemists is that the proteins they know are never extended in solution, but folded up, almost always, in globular conformation (see "The importance of cell water", this issue for a different, but possibly complementary view on cell water); and there is no evidence whatsoever that when such isolated proteins are in solution, they preferentially bind K+ over Na+.
Lings answer is that purified isolated proteins are not at all what they are like within the cell. Instead, within the cell, most, if not all proteins are extended so that the peptide bonds along their polypeptide chains are free to interact with the multiple layers of polarized water molecules, and their carboxylic side chains similarly are free to bind preferentially K+ over Na+. One reason may be the ubiquitous presence of ATP in the living cell.
Now comes perhaps Lings most original idea, and it makes a lot of sense. ATP -adenosine triphosphate - is the universal intermediate in all energy transformation processes, be it muscle contraction, protein synthesis, DNA synthesis, transport, etc. It was once erroneously regarded as the high energy intermediate, on account of its high energy phosphate bonds, which turned out not to be the case. Living protoplasm is full of ATP, which is bound to proteins at certain cardinal sites, according to Ling. These ATP-bound sites then induce changes in the electron density, ultimately of the entire polypeptide chain, including the side chains.
In the absence of ATP, proteins do tend to adopt secondary structures - alpha helix, or a beta pleated sheet - due to hydrogen bonding between peptide bonds in the same chain, which gives them a folded up conformation where they dont interact maximally with water. However, when ATP is bound to the cardinal site, it tends to withdraw electrons away from the protein chain, thereby inducing the hydrogen bonds to open up, unfolding the chain and enabling it to interact with water. This, Ling says, is the resting living state of the protoplasm, a low-entropy state thats highly organised, possessing what Schrödinger referred to as negative entropy (see Fig. 2).
Figure 2. Phase transition of protein on binding or releasing ATP.
It may be a misnomer to call the ATP-bound state of the protoplasm a resting state, as it is also full of stored energy ready to be released when ATP is hydrolysed to ADP. It so happens that ADP has a much lower tendency to bind to protein, so it comes off the cardinal site, and the protein naturally reverts to its folded state, an abrupt mechanical process that releases a lot of energy. It is a thermodynamically downhill or entropy-driven process because it produces disorder among the bound water molecules.
There could be other sites that bind molecules or ligands that have electron-donating tendency, in which case, an extended protein chain will abruptly adopt the folded up conformation, and at the same time, lose its ability to selectively bind K+, or even reverse its preference for binding Na+ over K+. The increase in electron density of the side-chain carboxylic groups favours the formation of ionic bonds, providing sufficiently strong attraction for the electropositive Na+ for it to give up its hydration shell.
No elaborate pumps or gates are needed to account for the high concentration of potassium and low concentration of sodium inside the cell, opposite to the situation in the extracellular medium. This is a plausible, testable hypothesis, although no one has yet put it to the test. Ling himself has lost his laboratory facilities at that point.
According to Ling, the abrupt transitions of state are what powers living activities. The living cell is an exquisite "electronic machine", where everything is done with the greatest of ease and the least bother, depending on the electron density in specific protein chains.
According to Ling, cell membranes do exist, but they are not the barriers to diffusion into and out of the cell, which, for far too long, has been regarded little more than a bag of enzymes in free solution that would instantly disintegrate were the membrane to disappear. Rather, the cell membrane is more like the skin of an apple which itself constitutes a phase similar to the bulk phase it encloses: the major constituents of membranes are also proteins that behave in a similar way as proteins in the cytoplasm. They too, preferentially bind K+ over Na+ in the resting state. Membrane potentials are local surface potentials, while action potentials simply reflect the changes of state that involves a release of bound water and the temporary exchange of Na+ for K+ bound to the carboxylic acid groups in the protein side chains.
The picture of what Ling has referred to as the resting living state with ATP and lots of associated water is very much like the liquid crystalline state that I and my colleagues have discovered in cells and organisms (see The Rainbow and The Worm, The Physics of Organisms ), which is another reason why I believe Ling may be largely correct. The living state - as opposed to the state of death in which ATP is exhausted, and rigor mortis sets in - is maximally hydrated by polarized layers of bound water, and hence flexible and full of energy. This idea of the truly living cell is beautifully brought to life in the inspired portraits produced by Ludwig Edelmann (see "Whats the cell really like?" this issue).
Article first published 28/10/04
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