Pteridines as nonretinal regulators of light-dependent melatonin biosynthesis.

Abstract
6-Formylpterin was purified by paper chromatography, and bovine pineal hydroxyindole-O-methyltransferase (S-adenosyl-L-methionine:N-acetylserotonin O-methyl-transferase; EC 2.1.1.4) was purified by flat-bed gel electrofocusing. Fractions of the methyltransferase with isoelectric points at pH 5.0, 5.7 and 5.2 were tested in the presence of 6-formylpterin and decreased activities were found. Because 6-formylpterin is a photolytic product of folic acid and decreased serum folic acid was reported in light-exposed men, pteridines may be involved in nonretinal effects of light on pineal melatonin biosynthesis. The metabolic pathway may be an evolutionary relic of primitive light responses of pigmentation mechanism.