Glutamate formyl- and formimino-transferase activities from pig liver

Formylglutamate:tetrahydrofolate formyltransferase (EC 2.1.2.6) from pig liver is not a separate entity, but represents a reaction catalyzed slowly by the active sites of formiminoglutamate:tetrahydrofolate formiminotransferase (EC 2.1.2.5). The two activities copurify through the stage of crystallization of the formiminotransferase and show very similar responses to heat inactivation and modification with diethylpyrocarbonate. Formylglutamate is a competitive inhibitor against formiminoglutamate, while glutamate is competitive against both the N-substituted glutamate substrates with similar values of Ki. Formyltransferase is a low activity with a Vmax of approximately 0.03% that of the formiminotransferase. All of the formyltransferase activity in liver extracts can be accounted for by the formiminotransferase enzyme.