Which two enzymes (using their common biochemical names) correspond to the transcript's 'enzyme A' and 'enzyme B' in the folic acid pathway?

• A. Enzyme A is dihydropteroate synthase (target of sulfonamides); enzyme B is dihydrofolate reductase (target of trimethoprim).
• B. Enzyme A is folylpolyglutamate synthase and enzyme B is folate transporter enzyme; these two are the classical antibiotic targets within folate metabolism.
• C. Enzyme A is thymidylate synthase and enzyme B is ribonucleotide reductase, as both are key folate-dependent enzymes targeted by sulfonamides and trimethoprim respectively.
• D. Enzyme A is dihydrofolate reductase and enzyme B is dihydropteroate synthase, because the pathway is reversed in bacteria compared with eukaryotes.

Answer: (A)