<prompt> Trimethoprim acts by:Inhibiting peptidyl transferase enzymeInhibiting dihydrofolate reductase enzymeInhibiting Dihydropteroate synthase enzymeBinds to 50s ribosomal unit and prevents protein synthesis  <response>: Trimethoprim, Methotrexate and pyrimethamine inhibits dihydrofolate reductase enzyme and prevents formation of Tetrahydrofolic acid and from Dihydrofolic acid. 