The Biosynthesis of Folic Acid

An enzyme that catalyzes the hydrolytic release of inorganic pyrophosphate from the triphosphate ester of 2-amino-4-hydroxy-6-(d-erythro-1',2',3'-trihydroxypropyl)-7,8-dihydropteridine (dihydroneopterin triphosphate), an intermediate in the biosynthesis of folic acid, has been partially purified from extracts of Escherichia coli and some of its properties have been described. The molecular weight of the enzyme, which has been named triphosphate pyrophosphohydrolase, has been estimated at 17,000. It will not use any of the nucleoside triphosphates as substrate; it exhibits a Km value of 11 µm for dihydroneopterin triphosphate; and Mg2+ is required for activity. The products of the action of the enzyme have been identified as PPi and dihydroneopterin monophosphate.