Trifunctional purine biosynthetic protein adenosine-3 is an enzyme that in humans is encoded by the GART gene.
This protein is a trifunctional polypeptide. It has phosphoribosylamineâÂÂglycine ligase (EC 6.3.4.13), phosphoribosylglycinamide formyltransferase (EC 2.1.2.2), AIR synthetase (FGAM cyclase) (EC 6.3.3.1) activity which is required for de novo purine biosynthesis.