ascorbic-acid and pterine-6-carboxylic-acid

The known functions of folate are to support one-carbon metabolism and to serve as photoreceptors for cryptochromes and photolyases. We demonstrate that 5-methyltetrahydrofolate (5-MTHF, the predominant folate in plasma) is also a potent, near diffusion limited, scavenger of singlet oxygen and quencher of excited photosensitizers. Both pathways result in decomposition of 5-MTHF, although ascorbate can protect against this loss. In the absence of photosensitizers, 5-MTHF is directly decomposed only very slowly by UVA or UVB. Although synthetic folic acid can promote DNA damage by UVA, submicromolar 5-MTHF inhibits photosensitization-induced strand breaks. These observations suggest a new role for reduced folate in protection from ultraviolet damage and have bearing on the hypothesis that folate photodegradation influenced the evolution of human skin color.

Topics: Ascorbic Acid; Chromatography, High Pressure Liquid; Depression, Chemical; DNA Breaks; DNA Damage; DNA, Superhelical; Folic Acid; Free Radical Scavengers; Oxidation-Reduction; Pentetic Acid; Photochemistry; Photosensitizing Agents; Pteridines; Rose Bengal; Singlet Oxygen; Sodium Azide; Superoxide Dismutase; Tetrahydrofolates; Ultraviolet Rays