Biopterin has two isomers (D- and L-biopterin). We sell only L-Biopterin. The hydrogenated forms of biopterin i.e. dihydrobiopterin and tetrahydrobiopterin are involved in many important biochemical functions in the human body, among which are the hydroxylation of tyrosine, phenylalanine and tryptophan. Biopterin has two isomers (D- and L-biopterin). We sell only L-Biopterin. The hydrogenated forms of biopterin i.e. dihydrobiopterin and tetrahydrobiopterin are involved in many important biochemical functions in the human body, among which are the hydroxylation of tyrosine, phenylalanine and tryptophan. 6-Biopterin is an oxidation product from the melanogenesis regulating cofactor (6R)5,6,7,8 tetrahydrobiopterin (6-BH4). In vitro, 6-Biopterin is cytotoxic to melanocytes. However, in vivo, 6-Biopterin is rapidly and sequentially reduced back to 6-GH4 via q-BH2. Recent studies suggest that 6-Biopterin among other pteridines may be a useful non-invasive biomarker for cancer