Sulfa medications primarily target which enzyme in the folate synthesis pathway?

Sulfa medications primarily target which enzyme in the folate synthesis pathway?

• A. Dihydropteroate synthase (PABA --> DHF)
• B. Dihydrofolate reductase (DHF --> THF)
• C. Dihydrofolate synthase
• D. Thymidylate synthase

Answer: (A)

Sulfa drugs work by mimicking PABA and blocking the bacterial enzyme that converts PABA into dihydropteroate, the first committed step in folate synthesis. This enzyme is dihydropteroate synthase. By inhibiting it, bacteria can't make dihydrofolate and, downstream, tetrahydrofolate, which are needed to synthesize thymidylate and purines for DNA. Without THF, DNA synthesis slows and bacterial growth is halted. Humans don’t synthesize folate and obtain it from the diet, so this bacterial enzyme is not present in our cells, allowing selective antibacterial action. When used with trimethoprim, the next step is also blocked by inhibiting dihydrofolate reductase, enhancing the effect.

Sulfa drugs work by mimicking PABA and blocking the bacterial enzyme that converts PABA into dihydropteroate, the first committed step in folate synthesis. This enzyme is dihydropteroate synthase. By inhibiting it, bacteria can't make dihydrofolate and, downstream, tetrahydrofolate, which are needed to synthesize thymidylate and purines for DNA. Without THF, DNA synthesis slows and bacterial growth is halted. Humans don’t synthesize folate and obtain it from the diet, so this bacterial enzyme is not present in our cells, allowing selective antibacterial action. When used with trimethoprim, the next step is also blocked by inhibiting dihydrofolate reductase, enhancing the effect.