Reformulation of the Michaelis-Menten Equation: How Enzyme-Catalyzed Reactions Depend on Gibbs Energy.

Textbooks in biochemistry universally present a simplified two-step reaction mechanism for enzyme-catalyzed reactions. Step 1 is formation of an enzyme–substrate complex and step 2 is breakdown of the complex to form product. It is usually emphasized that the rate of the second step is increased when the enzyme raises the Gibbs energy of the complex and lowers the Gibbs energy of the second transition state. In this article the well-known Michaelis–Menten rate law for enzyme-catalyzed reactions is combined with the Arrhenius equation to show how the rate of reaction depends on Gibbs energies of both the first and second transition states (G2 and G4, respectively) as well as the Gibbs energy of the enzyme–substrate complex (G3). In this way it becomes easier to see the effect of the first step of the reaction mechanism on the overall reaction rate. In general the maximum velocity of the reaction (vm) depends solely on the activation energy of the second step (G4 - G3) whereas the Michaelis constant (KM) de...