The PTS gene encodes 6-pyruvoyl-tetrahydropterin synthase (EC 4.6.1.10), an enzyme involved in the biosynthesis of tetrahydrobiopterin (BH4), an essential cofactor for aromatic amino acid hydroxylases, such as hepatic phenylalanine hydroxylase (PAH), tyrosine hydroxylase (TH), and tryptophan hydroxylase (TPH1), as well as for all 3 forms of nitric oxide synthase. The deduced 145-residue protein has a molecular mass of 16.4 kD. The human amino acid sequence showed 82% identity with the rat liver sequence. Expression of the cDNA in E. coli yielded the active enzyme and showed immunoreactivity with antibodies against the rat liver PTS.PTS gene spans about 8 kb and contains 6 exons, as revealed by DNA sequence analysis.