Mammalian glycinamide ribonucleotide transformylase: purification and some properties.

Glycinamide ribonucleotide transformylase, the first of the two formyl group transferases of de novo purine biosynthesis requiring 10-formyltetrahydrofolate, has been purified 1500-fold, nearly to homogeneity, from the murine lymphoma cell line L5178Y. Purification of the enzyme was facilitated by the use of a gelatin protease "affinity" resin. This mammalian enzyme is a monomer of approximate Mr 110 000. The kinetic studies are consistent with a sequential reaction mechanism and yield Michaelis constants of 0.4 mM for the substrate, glycinamide ribonucleotide, and 0.25 microM for the cofactor analogue 10-formyl-5,8-dideazafolate. A minimum Vmax of 2 mumol/(min . mg) was obtained for the purified enzyme, from which a turnover number of 4 s-1 was calculated.