Bke2 Biochemistry Lectures

Lecture 14: Enzyme Kinetics
Reading material: Horton, Chapters 5-6 (Stryer, Chapter 8).

Abstract: A common method of analyzing enzyme activity is by Michaelis-Menten kinetics. A combined rate constant K_M, the Michaelis constant, is the concentration of the substrate when half of the maximum speed is achieved. Since K_M is also the concentration of substrate at which half of the active sites are filled it is a measure of the enzyme's affinity for the substrate. The turnover number, kcat, is in the simple case the first-order rate constant for product formation. kcat/K_M is an apparent second-order rate constant that refers to the properties and the reactions of the free enzyme and free substrate. This value is a measure of the catalytic efficiency of the enzyme for a given substrate and its upper limit is set by the rate of diffusion. Several enzymes work at velocities close to this speed. Enzyme kinetics is used as a quantitative analysis of enzyme activity and as a means of understanding the mechanism of chemical catalysis.

Key concepts:
Activation energy
Transition state relationship to rates of reaction
Michaelis-Menten model and equations, ES complex
Lineweaver-Burk (double reciprocal) plot
K_M vs. Kd, Vmax, kcat
kcat/K_M is a measure of catalytic efficiency
Reversible and irreversible inhibition (inactivation)
Competitive & non-competitive inhibition
Transition state analog

Links:
The MIT hypertext book: Enzymes

Lecture index

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