Question

which of the following statements is/are true concerning non competitive (allosteric) inhibition

a. binding of the inhibitor to the regulatory (allosteric) site reduces the activity of the enzyme

b. binding if the substrate to the active (substrate) site prevents binding of the inhibitor to the allosteric site

c. it often occurs when the product(s) of a biochemical pathway accumulate

d. all of the above

e. A and C

Answer 1

Ans: Allosteric inhibitors bind to the enzyme at a site different from the active site. It binds to the regulatory site on the enzyme and upon binding to the regulatory site the inhibitor induces the conformational change at the active site such that substrate cannot bind to the enzyme any longer.

It has been found that the allosteric enzyme exists in two states: T state (low-affinity state for substrate) and R state (high-affinity state for substrate). Substrate bind to R state whereas inhibitor binds to the T state and inhibits the binding of the substrate.

a. binding of the inhibitor to the regulatory (allosteric) site reduces the activity of the enzyme - True, as discussed, the allosteric inhibitor binds to the allosteric site other than the active site and induces a conformational change that prevents the binding of the substrate. When the substrate will not bind to the enzyme inhibitor, it will reduce the activity of the enzyme.

b. binding of the substrate to the active (substrate) site prevents binding of the inhibitor to the allosteric site - False, allosteric inhibition differs from competitive inhibition. Inhibitors in this case binds to the site other than the active site. Hence, the binding of the substrate will not interfere with the binding of the inhibitor.

c. it often occurs when the product(s) of a biochemical pathway accumulate - True, there are many examples of allosteric inhibition which regulates the enzyme in the metabolic pathway allosterically. Here, the product of the biochemical pathway binds to the enzyme at an allosteric site to regulate the formation of the product.

For example, high levels of ATP results in the binding of ATP to the pyruvate kinase and inhibits the enzyme allosterically thereby regulating glycolysis.

d. all of the above - Because option b is incorrect, all options are not true.

e. A and C- True. As discussed.

As explained, option E is correct

I hope this will help you