| Abstract: | The overall rate equation for a reaction sequence consisting of a pre-equilibrium and ratedetermining steps should not be
derived on the basis of the concentration of the intermediate product (X). This is apparently indicated by transition state
theory (as the path followed to reach the highest energy transition state is irrelevant), but also proved by a straight-forward
mathematical approach. The thesis is further supported by the equations of concurrent reactions as applied to the partitioning
of X between the two competing routes (reversal of the pre-equilibrium and formation of product). The rate equation may only
be derived rigorously on the basis of the law of mass action. It is proposed that the reactants acquire the overall activation
energy prior to the pre-equilibrium, thus forming X in a high-energy state en route to the rate-determining transition state. (It is argued that conventional energy profile diagrams are misleading and need
to be reinterpreted.) Also, these arguments invalidate the Michaelis-Menten equation of enzyme kinetics, and necessitate a
fundamental revision of our present understanding of enzyme catalysis. (The observed “saturation kinetics” possibly arises
from weak binding of a second molecule of substrate at the active site; analogous conclusions apply to reactions at surfaces). |
