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Contributed Paper

Enzyme Function: Random Events or Coherent Action ?

John Grant Watterson


Abstract

This article compares the traditional statistical approach to our understanding of enzyme function with that of the opposing structuralist view. To introduce this investigation, attention is drawn to several points regarding the statistical approach: firstly, it is not possible to reconcile values of thermodynamic and kinetic parameters obtained in solution studies with protein stability and enzymic activity as known in the cell; secondly, the sequence of reactions in metabolic pathways would resemble a collection of average events, in which each substrate molecule entering the initial step of the pathway has a defined probability of becoming the final product at the end, whereas the cell requires certainty; thirdly, the basic assumption that the role of water is that of a random background solvent does not fit the biologists' picture of the cytoplasm, which can adopt any of several active physical states such as the extending, contracting, streaming, gelling; and fourthly, a random background solvent would necessarily play a destructive rather than a constructive role in the cell's mechanical processes.

In contrast, the structuralist approach is based on the cluster model in which water and protein are equal partners in cell function. Enzyme complexes are large protein assemblies which are stabilized by internal tensile forces. These forces arise from structural, as opposed to thermal energy, and simple work cycles establish that this energy can be converted into work by machines exerting tension. This result is used to develop a speculative model of enzyme activity. In the model, catalysis and product translocation steps are synchronized by a pressure-tension switch operating at the water-protein interface and powered by osmotic energy available in the solvent.

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