6-pyruvoyl tetrahydropterin synthase (PTPS). Folate derivatives are essential cofactors in the biosynthesis of purines, pyrimidines, and amino acids, as well as formyl-tRNA. Mammalian cells are able to utilize pre-formed folates after uptake by a carrier-mediated active transport system. Most microbes and plants lack this system and must synthesize folates de novo from guanosine triphosphate. One enzyme from this pathway is PTPS which catalyzes the conversion of dihydroneopterin triphosphate to 6-pyruvoyl tetrahydropterin. The functional enzyme is a hexamer of identical subunits.