Question

1. Which of these is true of competitive enzyme inhibitors? Select all correct answers.

A. Competitive inhibitors lower the enzyme's kcat

B. Competitive inhibitors often resemble the substrate

C. Competitive inhibitors bind at the same site as the enzyme's substrate

D. Competitive inhibitors permanently inhibit the enzyme, even after removal

E. Competitive inhibitors effectively raise the enzyme's Km

2. An antibody-antigen pair is found to bind with a K_d of 25 nM. Replacing three Phe at the binding site with Tyr is found to raise the K_d to 152 nM. Which of these is a possible explanation for why this happens? Select all possible answers.

A. Binding to the antigen is driven mostly by ionic interactions

B. Binding to the antigen is driven mostly by hydrogen bonding

C. Binding to the antigen is driven mostly by the hydrophobic effect

D. The replacement of Phe with Tyr has changed the pH of the mixture

E. Replacement of Phe with Tyr alters the shape of the binding surface

Answer 1

1) competitive inhibitor binds to the enzyme and hence prevents the substrate from binding.

competitive inhibitor lowers the enzyme kcat. kcat means the turnover number that is the number of times the enzyme converts substrate to product per unit time. Since the inhibitor binds with enzyme it lowers the turnover number.

Competitive inhibitor resembles with that of the substrate and hence could bind effectively with the enzyme.

It binds at the same site and it permanently inhibits the enzyme. They raise the km. The rate of reaction and the substrate concentration depend upon affinity of the enzyme for the substrate and is expressed as km. The increase in km means low affinity for substrate. So, when the inhibitor binds with the enzyme the km increases.

So, all are correct answers.