GCH-1 catalyzes the conversion of GTP to D-erythro-7,8-dihydroneopterin triphosphate, the first and rate-limiting step in tetrahydrobiopterin (BH4) biosynthesis. The final product (BH4) is an essential co-factor for three aromatic amino acid monooXygenases (F,Y, and W). Isoform GCH-1 is the functional enzyme.The synthetic peptide used to raise the antibody Cat. No. 250680 is selected from a sequence within the N-term region of human GTP-CH-1. For blocking experiments, a 10 to 100 fold molar excess to antibody is recommended.