Question

The presence of blockulin reduces the amount of product made in an enzyme-catalyzed reaction. Adding more substrate has NO effect. What form of regulation is performed by blockulin?

Answer 1

Blockulin would be an ALLOSTERIC inhibitor of the enzyme. An allosteric inhibitor is something that binds to an enzyme somewhere OTHER than its active site. This binding causes a conformational (shape) change of the actual active site, preventing the enzyme from interacting with its substrate - this means changing the amount of substrate will have no effect, because the substrate cannot bind!

The other main type of regulation is COMPETITIVE inhibition. In this case, the inhibitor actually binds to the active site of the enzyme and therefore COMPETES with the substrate for this position. Increasing the amount of substrate will increase the likelihood that the substrate, and not the inhibitor, will be the one to bind to the active site. Therefore, increasing the substrate concentration will have an effect.