Enzyme Kinetics

Competitive Inhibition


Competitive inhibitors bind at the substrate binding site, i.e. they compete with the substrate for the active site.

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In this kind of inhibition there is a competition between the inhibitor and the substrate for the same binding site. Thus if one raises the concentration of the substrate high enough the effect of the inhibitor will be overcome. That is, the Vm can still be reached in spite of the presence of the inhibitor, i.e. it is unchanged. On the other hand, the Km is changed. It is diagnostic of competitive inhibitors that they cause an alteration of the Km but the Vm is unchanged.

Competitive inhibitors are quite common in nature. They often bear obvious structural relationships to the substrate. It is common for products of a reaction to be competitive inhibitors, and this is a form of biological control as it prevents excessive build up of the product.

Invertase, or alpha-D-glucosidase, is an enzyme which hydrolyzes sucrose into its component monosaccharides, glucose and fructose. However, glucose is a competitive inhibitor of invertase, alpha-D-glucosidase, or beta-fructofuranosidase. This is one of the simplest forms of biological control. When the concentration of product builds up it turns off its own formation.

glucose-fructose   <->  glucose + fructose


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