Involved in the de novo purine biosynthesis (PubMed:8501063, PubMed:8117714, PubMed:9184151). Catalyzes the transfer of formate to 5-phospho-ribosyl-glycinamide (GAR), producing 5-phospho-ribosyl-N-formylglycinamide (FGAR) (PubMed:8501063, PubMed:8117714, PubMed:9184151). Formate is provided by PurU via hydrolysis of 10-formyl-tetrahydrofolate (PubMed:8226647). PurT is also able to cleave acetyl phosphate and carbamoyl phosphate to produce ATP with acetate and carbamate, respectively (PubMed:8117714, PubMed:9184151). ATP + formate + N(1)-(5-phospho-beta-D-ribosyl)glycinamide = ADP + H(+) + N(2)-formyl-N(1)-(5-phospho-beta-D-ribosyl)glycinamide + phosphate acetate + ATP = acetyl phosphate + ADP ATP + carbamate = ADP + carbamoyl phosphate kcat is 37.6 sec(-1) for transformylase activity (at pH 8). kcat is 0.309 sec(-1) for acetate kinase activity (at pH 8). Purine metabolism; IMP biosynthesis via de novo pathway; N(2)-formyl-N(1)-(5-phospho-D-ribosyl)glycinamide from N(1)-(5-phospho-D-ribosyl)glycinamide (formate route): step 1/1. Homodimer. Mutant defective in both purN and purT requires an exogenous purine source for growth. Belongs to the PurK/PurT family.