Enzyme Kinetics
Part II. Enzyme Inhibition
IV. Evaluating Enzyme Inhibitors to determine type and their Ki.
To determine what type an inhibitor is:
1. Find Km and Vmax for uninhibited from 1/Vo vs 1/[S] plot.
2. On same graph find Km' and Vmax' for inhibited reaction.
A. If Vmax = Vmax' then inhibitor is competitive type.
(Vmax and Vmax' should not be more than 10% different)
B. If Vmax does not equal Vmax', then if Km = Km', inhibitor is non competitive type.
After finding inhibitor type, then use equations to calculate Ki. Ki is a binding constant for inhibitor to the enzyme. Ki has same units as the [I]. If [I] = mM, then Ki = mM.
Equations used for calculating Ki values:
Figure 9A. Equation for Competitive Inhibitor.
Figure 9B. Equation for Non-Competitive Inhibitor.
Rearrange these equations to solve for Ki.
Summary:
Enzyme inhibitors - two types
I. Competitive
II. Non competitive
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©Wilbur H. Campbell, 1995; wcampbel@mtu.edu