Biochemistry

Lecture 15 (Handout): Enzyme Inhibition Kinetics

Example of Data Analysis for Competitive Inhibition

1. Double Reciprocal Plot: 1/v_o vs. 1/[A].
   
   The above data are those shown on the Enzyme Inhibition: Answer Sheet Example page. The bottom (blue) line corresponds to the calculated 1/v_o values without added inhibitor. V_max = 0.5 mM/min; K_M = 2 mM.
   The top two lines (green and red) correspond to the curves with 2 mM and 5 mM added [I]. The common intercept and slopes that increase with increasing [I] is characteristic of competitve inhibition.
2. Secondary Plot: Slopes vs. [I].
   
   The slopes from the above double reciprocal plot are plotted in a secondary plot (or "replot") vs. the [I]'s used.
   The intercept of this graph is, K_M/V_max.
   The slope of this graph is, K_M/(V_maxK_I).
   Thus, K_I = Int/Slope = 3 mM.

Secondary Plots are also used to determine K_I values for noncompetitive and uncompetitive inhibition. In these cases, the slopes and/or intercepts of the primary plots are replotted vs. [I] as shown above.

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