Involved in the biosynthesis of tetrahydrobiopterin, an essential cofactor of aromatic amino acid hydroxylases. Catalyzes the transformation of 7,8-dihydroneopterin triphosphate into 6-pyruvoyl tetrahydropterin. 7,8-dihydroneopterin 3'-triphosphate = 6-pyruvoyl-5,6,7,8-tetrahydropterin + H(+) + triphosphate Binds 1 zinc ion per subunit. Cofactor biosynthesis; tetrahydrobiopterin biosynthesis; tetrahydrobiopterin from 7,8-dihydroneopterin triphosphate: step 1/3. Homohexamer formed of two homotrimers in a head to head fashion. The active site is at the interface between 2 subunits. The proton acceptor Cys is on one subunit, and the charge relay system is on the other subunit. Belongs to the PTPS family.