transformylase

Transformylase is a broad term for enzymes that transfer a formyl group from a one-carbon donor, most commonly 10-formyltetrahydrofolate (10-formyl-THF), to an acceptor molecule. In cellular metabolism these enzymes participate primarily in purine biosynthesis and, in bacteria, in translation initiation, linking formyl transfer to folate-dependent one-carbon metabolism.

In de novo purine biosynthesis, glycinamide ribonucleotide transformylases (GAR transformylases) catalyze the formylation of glycinamide ribonucleotide (GAR) to formylglycinamide ribonucleotide (FGAR). Some organisms have PurN as the canonical folate-dependent GAR transformylase, while others use PurT, which can utilize formyl phosphate as the donor. A separate enzyme, AICAR transformylase (PurH), catalyzes the formylation of aminoimidazole carboxamide ribonucleotide (AICAR) to FAICAR and often has an additional IMP cyclohydrolase activity as part of a bifunctional protein.

In translation initiation, methionyl-tRNA formyltransferase adds a formyl group from 10-formyl-THF to methionyl-tRNAiMet, producing formylmethionyl-tRNAiMet, the initiator tRNA used by many bacteria and organelles to start protein synthesis.

Transformylase activity depends on folate-derived one-carbon units, connecting their function to the cellular folate pool. Inhibitors that deplete 10-formyl-THF, including antifolate drugs, can impair these enzymes and disrupt purine biosynthesis or translation initiation.

Transformylases are widely found in bacteria and organelles with folate-dependent metabolism; their presence and specific forms vary among species, reflecting differences in metabolic pathways.