Theoretical calculations on neutral model substrates of enzyme catalysis exhibit relatively high potential energy barriers with respect to values derived from experimental rate constants fitted to conventional expressions. A statistical theory based on the coupling of vibrational modes of the protein to the reaction coordinate affords a new expression for the unimolecular rate constant. Rate constants computed with the proposed theory are many orders of magnitude greater than the corresponding values given by traditional Arrhenius-type laws for a given potential energy barrier and temperature. Within this model, the hypothesis of a lowering of the potential energy barrier caused by specific interactions at the active site is no longer necessary. The dependence of the unimolecular rate constant by the energy barrier and temperature is given by the ratio of the incomplete and the complete gamma functions of Euler. The performance of the proposed model is tested against experimental rate constant for the hydrolysis of N-acetyl-L-tryptophan ethyl ester and N-acetyl-L-tyrosine ethyl ester catalyzed by alpha-chymotrypsin. The experimentally accessible quantity (T/beta)partial derivative(T) In k may serve to discriminate between the conventional model (reduction of the potential energy barrier) and catalysis through dynamical coupling.