Michaelis-Menten Equation

We will first consider the effect of substrate concentration on rate, because enzyme kinetics began with this. Enzyme kinetics really began with the derivation, in the early 1900s, of the Michaelis-Menten Equation, which describes the relationship between rate and substrate concentration for the reaction:

It was assumed that the reverse reaction of was insignificant because we are concerned with initial rates, where P is negligible; and therefore the reverse, , is also negligible. The rates were then combined to

then it can be shown that

There are several assumptions inherent in their derivation. First they assumed that << and therefore that the last reaction, the breakdown of ES to E+P can be ignored. This then sets up an equilibrium

and this is called The Equilibrium Assumption (Michaelis and Menten). One result of this assumption is that

The is the dissociation constant for the ES complex to E + S, and that as such it is inversely proportional to the strength of binding of E and S. A high means a low affinity and a low means a high affinity. Note that the is the dissociation constant only under these conditions.

The Thomas Jefferson University web site, its contents and programs, is provided for informational and educational purposes only and is not intended as medical advice nor is it intended to create any physician-patient relationship. Please remember that this information should not substitute for a visit or a consultation with a health care provider. The views or opinions expressed in the resources provided do not necessarily reflect those of Thomas Jefferson University, Thomas Jefferson University Hospital, or the Jefferson Health System or staff.