Enzyme Inhibition

The Lineweaver-Burk equation

 

As my first post this week was quite long, I’ll make my second a short one and save you some reading time. I’m pretty sure we’ve all done CHEM2002, and have learnt about enzyme competition before. This chapter mentions competitive inhibition and noncompetitive inhibition. To refresh our memories, competitive inhibition is where the inhibitor molecule binds to the same site as the enzyme’s substrate. Thus they are in direct competition with each other at the binding site.

Noncompetitive inhibition is where the enzyme has two binding sites, which are effectively mutually exclusive. When the inhibitor binds to its binding site, the enzyme cannot bind the substrate any more, and thus the reaction again is inhibited. We learnt a third kind of inhibition, uncompetitive inhibition. This is where the inhibitor binds to the enzyme substrate complex.

These three kinds of inhibition have different effects on the Lineweaver-Burk plot as the inhibitor concentration is increased. If the inhibition is competitive, the y-intercept of the Lineweaver-Burk plot is constant, but the gradient changes. If the inhibition is noncompetitive, the x-intercept of the plot is constant, but the slope changes. If the inhibition is uncompetitive, the gradient is constant, but the y-intercepts changes (it increases). This means that competitive inhibition does not affect the vmax of the reaction and noncompetitive inhibition does not affect Km. Uncompetitive inhibition lowers both the Km and vmax.