ber das Vorkommen lichtempfindlicher, fluorescierender Substanzen in verschiedenen Geweben von Rinderaugen

Inhibition of avian and mammalian hydroxy-indole-o-methyl-transferase (HIOMT) with low molecular weight fractions of mammalian pineal glands

Partially purified fractions from sheep pineal gland extracts, which show a fluorescence like pteridines, were shown to suppress the enzyme hydroxy-indole-o-methyltransferase (HIOMT) isolated from avian pineals and retinas. The results described demonstrate that the mechanism of inhibition of HIOMT activity is independent of the species and organ. A blocking effect was found in experiments whether retinal or pineal HIOMT were used and the effect was found as well with bovine HIOMT. It is shown that low molecular weight molecules show inhibitory activity and accompany the high molecular weight enzyme HIOMT.

Pteridines as nonretinal regulators of light-dependent melatonin biosynthesis

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 one of the photolytic products of folic acid and decreased serum folic acid has been reported in light-exposed men, we suggest that pteridines may be involved in nonretinal effects of light on pineal melatonin biosynthesis. It may be that this metabolic pathway is an evolutionary relic of primitive light responses of pigmentation mechanism.