Noncompetitive inhibition slope effect

These three classes of inhibition can be distinguished by virtue of the effect of variations in inhibitor concentration on the slopes and intercepts of reciprocal plots. For competitive inhibition only the slope varies. For uncompetitive inhibition only the intercept varies, while for noncompetitive inhibition both the slope and the intercept vary. 

Noncompetitive inhibition results when the inhibitor binds to both E and ES. Here, both the slopes (Km/Vmax) and intercepts (1/Vmax) exhibit an effect of the inhibitor. The lines of different inhibitor concentration intersect (their slopes are different), but they do not intersect on the y axis (their intercepts are different). 

We shall turn now to much more realistic cases of bisubstrate reactions. The proper way to study a substrate inhibition in bisubstrate reactions is to vary a noninhibitory substrate, at differing high levels of the inhibitory one and see whether the slopes, intercepts, or both of reciprocal plots show the inhibitory effects (Cleland, 1979). These cases are then called competitive, uncompetitive, and noncompetitive substrate inhibition, respectively. 

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