Biosynthesis of neopterin, sepiapterin, and biopterin in rat and human ocular tissues.

Neopterin, sepiapterin, and biopterin synthesis by lens, retina, and ciliary body-iris of rat and human indicates pteridine formation from their precursor, GTP. The pteridine biosynthesis was higher in the retina (neopterin 422 +/- 27, 260 +/- 24; sepiapterin 135 +/- 12, 118 +/- 14; biopterin 76 +/- 10, 68 +/- 8 nanomoles/g soluble protein/hr, in rat and human, respectively) than in the ciliary body-iris and lens. The light-sensitive pteridines may protect eye tissues against the effects of sunlight in addition to their role in the hydroxylation of aromatic amino acids.