Mammalian glycinamide ribonucleotide transformylase. Kinetic mechanism and associated de novo purine biosynthetic activities.

Glycinamide ribonucleotide transformylase catalyzes the conversion of glycinamide ribonucleotide and 10-formyltetrahydrofolate to formylglycinamide ribonucleotide and tetrahydrofolate. The enzyme purified from the murine lymphoma cell line L5178Y also catalyzes two other de novo purine biosynthetic activities, glycinamide ribonucleotide synthetase and aminoimidazole ribonucleotide synthetase. The transformylase reaction shows a 1:1 stoichiometry for substrate utilization and an optimum rate between pH 7.9 and 8.3. Initial velocity and dead-end inhibition patterns indicate that the kinetic mechanism of the transformylation reaction is ordered-sequential, with 10-formyltetrahydrofolate binding first. alpha, beta-Hydroxyacetamide ribonucleotide (alpha, beta-N-(hydroxyacetyl)-D-ribofuranosylamine) is shown to be an inhibitor of the transformylase, competitive against glycinamide ribonucleotide.