THE TRANSFORMYLASE ENZYMES OF DE-NOVO PURINE BIOSYNTHESIS

Formyl transfer reactions play a key role in the construction of the p urine heterocycle during de novo purine biosynthesis. Formylation is c atalyzed early in the pathway by the purN glycinamide ribonucleotide t ransformylase (GAR Transformylase, EC 2.1.2.2) in a tetrahydrofolate-d ependent manner and also by the purT GAR transformylase in a tetrahydr ofolate-independent manner in bacteria. Late in the pathway, 5-aminoim idazole-4-carboxamide ribonucleotide transformylase (AICAR Transformyl ase, EC 2.1.2.3) catalyzes the second and final formylation involved i n purine nucleotide biosynthesis. This article summarizes the salient properties and mechanistic knowledge on the transformylases with speci al emphasis on the mechanism of the purN GAR transformylase as explore d by mutagenesis studies.