Inhibitory Effect of Xanthopterin upon the Formation of Melanin in vitro

Abstract

IT is already known that riboflavin, under irradiation of shorter light waves, accelerates the autoxidative production of melanin from 3,4-dihydroxyphenylalanine (dopa)¹, while pteridine derivatives are reported by many authors² to be inhibitory, more or less, to the activity of the milk xanthine oxidase, and Totter³ says that this inhibition might be due to an antagonistic interaction of pteridine and isoalloxazine rings. Since my co-workers and I have been interested in the reactions of melanin and xanthopterin-like pigments in the silkworm⁴, and also in a seemingly similar phenomenon in the wasp⁵, these facts led me to carry out some experiments on melanin formation in vitro, using riboflavin and xanthopterin, upon the supposition that the acceleration of the autoxidation of 3,4-dihydroxyphenylalanine by the former may possibly be cancelled by the latter. During the course of these experiments, however, it was discovered that xanthopterin alone will inhibit the autoxidation of dihydroxyphenylalanine.