Function: Random Events or Coherent Action ?
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.
Full pdf file: Watterson.pdf
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