Enzyme Inhibition (Part 2 of 3) - Noncompetitive Inhibitors

Moof's Medical Biochemistry Video Course: http://moof-university.thinkific.com/...

Questions Answered in This Video:

What are noncompetitive inhibitors, and what is mechanism by which they act?
How do noncompetitive inhibitors affect the values of KM and VMAX?
How do noncompetitively inhibited reactions look on the hyperbolic graph and Lineweaver-Burk plot?

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Video Content Summary:

Noncompetitive inhibitors, unlike competitive inhibitors, do not bind at the active site. They bind a site elsewhere on the enzyme. Thus, they can bind free enzyme OR the enzyme-substrate complex. So, the enzyme-substrate complex, the enzyme-noncompetitive inhibitor complex, and the enzyme-substrate-noncompetitive inhibitor complex can all potentially form. Of course, as long as the noncompetitive inhibitor is bound, the enzyme will not be able to convert substrate into product.

Since a noncompetitive inhibitor binds at a site other than the active site and does not have an impact on whether or not substrate can bind, the affinity of enzyme for substrate is not changed, and the KM value remains unchanged. However, the effect of a noncompetitive inhibitor cannot be overcome by increasing substrate concentration, and as long as there are noncompetitive inhibitors present, there will be a smaller number of functional enzymes, relative to an uninhibited case. Less functional enzymes means lower rate of catalysis and a lower VMAX.

The effects of a noncompetitive inhibitor on an enzyme-catalyzed reaction are depicted in a variety of ways in the video, and it is shown what happens to the hyperbolic graph and the Lineweaver-Burk plot, otherwise known as the double reciprocal plot.