In Reactions Catalyzed by Allosteric Enzymes

Question

In reactions catalyzed by allosteric enzymes
A) substrate, activators, and inhibitors all compete for the same binding site on the enzyme.
B) there is no distinction between catalytic and regulatory subunits.
C) the presence of an activator makes the plot of reaction rate against substrate concentration less cooperative.
D) the presence of an inhibitor makes the plot of reaction rate against substrate concentration less cooperative.

Accepted Answer

Allosteric enzymes have binding sites that are separate from the catalytic site called allosteric sites. Activators bind to the allosteric site and stabilize the enzyme in a conformation that has a higher affinity for substrate at the catalytic site. This makes the plot of reaction rate against substrate concentration more cooperative. Inhibitors bind to the allosteric site and stabilize the enzyme in a conformation that has a lower affinity for substrate at the catalytic site. This makes the plot of reaction rate against substrate concentration more sigmoidal. Therefore, choice C is the best answer because it is the opposite of what happens in the presence of an activator.