Which one of the following enzymes of nucleotide metabolism is correctly paired with its pharmacologic inhibitor?

A. Dihydrofolate reductase-methotrexate

B. Inosine monophosphate dehydrogenase-hydroxyurea

C. Ribonucleotide reductase-5-fluorouracil

D. Thymidylate synthase-allopurinol

E. Xanthine oxidase-probenecid

A. Dihydrofolate reductase-methotrexate

Explanation:

Dihydrofolate reductase is an enzyme that reduces dihydrofolic acid to tetrahydrofolic acid. Methotrexateis its inhibitor. It interferes with folate metabolism by acting as a competitive inhibitor of the enzyme.

Since folateis necassary for rapid dividing cells, such as cancer cells, methotrexate can be used as anticancer drug that inhibits DHFR.