Appendix J: Enzyme Inhibitio Enzyme Inhibition Vmax: The maximum rate of the reaction Km: The amount of substrate needed for the enzyme to work half as fast as it is capable of. !Km = ¯enzyme-substrate affinity ¯Km = ! enzyme-substrate affinity Competitive Inhibition Uncompetitive Inhibition Noncompetitive Inhibition Vmax no change !KM ¯Vmax ¯KM ¯Vmax KM no change An uncompetitive inhibitor binds only to the enzyme–substrate complex. A noncompetitive inhibitor binds at the allosteric site, away from the active site. It does NOT prevent the substrate from binding to the active site. A competitive inhibitor binds at the active site and thus prevents the substrate from binding. Lineweaver-Burk Plots Lineweaver-Burk Plots • A double-reciprocal plot of ! " vs. ! [$] slope=, -. "./0 • Left side of the graph is theoretical because you can’t have negative substrate or velocity higher than Vmax • Vmax and Km can be more precisly calculated using Lineweaver-Burk because you are extrapolating out theoretical values. • Michaelis-Menton curves show observed values only, not theoretical values. This makes calculations using Michaelis-Menton less accurate than Lineweaver-Burk. • Lineweaver-Burk allows the different types of inhibition to be visualized more clearly. Michaelis-Menten Curves Vmax, Vmax V = reaction rate Competitive Inhibitor: Vmax no change, !KM ! 1 Uncompetitive Inhibitor: ¯Vmax, ¯KM Vmax Vmax 1 max Vmax ! 1 ! 1 Vmax Noncompetitive Inhibitor: ¯Vmax, KM no change Vmax Km Km Km Km [S] = substrate concentration