Abstract
Summary
The inhibitory effect on melanin formation of aqueous extracts of isolated human epidermis and of homogenates of rabbit skin was found' to be due to heat-stable, dialyzable, non-protein-like sulfhydryl compounds which were counteracted by cupric ions and p-chloromercuribenzoic acid. A direct relationship was found between the -SH concentration and the inhibitory power of extracts of human epidermis. Ultraviolet irradiation caused an immediate decrease in the amount of water-extractable -SH compounds of the skin of colored rabbits. No such decrease could be observed in albino animals. These findings support the previously advanced theory that pigment forming stimuli cause pigmentation by oxidizing or destroying the sulfhydryl compounds of the epidermis, whereupon the enzyme can freely act on the melanin precursor.
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