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  Home > JCE Print > Journal of Chemical Education > Issues > 2007  > January  >
In the Classroom
Advanced Chemistry Classroom and Laboratory
Reformulation of the Michaelis–Menten Equation: How Enzyme-Catalyzed Reactions Depend on Gibbs Energy
Brian J. Bozlee
Department of Chemistry, Hawaii Pacific University, Kaneohe, HI 96744-5297
Cover
January 2007
Vol. 84 No. 1
p. 106
Abstract
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) depends on all three Gibbs energies (G2, G3, and G4). Both vm and KM affect the overall rate of reaction.

See Correction.

Supplement
Discussion of the temperature dependence of the Gibbs terms in the Arrhenius equation is available.
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Citation
Bozlee, Brian J. J. Chem. Educ. 2007, 84, 106.
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Keywords
Biochemistry; Enzymes; Kinetics; Physical Chemistry; Upper-Division Undergraduate
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History
Created:
Last Updated:
12/5/2006
5/1/2007
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