  A relationship between the preexponent of the rate constant and the
distribution over activation barrier energies for enzymatic/protein reactions
is revealed. We consider an enzyme solution as an ensemble of individual
molecules with different values of the activation barrier energy described by
the distribution. From the solvent viscosity effect on the preexponent we
derive the integral equation for the distribution and find its approximate
solution. Our approach enables us to attain a twofold purpose. On the one hand
it yields a simple interpretation of the solvent viscosity dependence for
enzymatic/protein reactions that requires neither a modification of the
Kramers' theory nor that of the Stokes law. On the other hand our approach
enables us to deduce the form of the distribution over activation barrier
energies. The obtained function has a familiar bell-shaped form and is in
qualitative agreement with the results of single enzyme kinetics measurements.
General formalism is exemplified by the analysis of literature experimental
data.
