SUMMARY: was studied in a defined medium. When tyrosine was added to the medium a brown-black pigment was synthesized; without tyrosine, only a trace of this pigment was detected. Growth was the same with or without tyrosine. The addition of (2-C) DL-tyrosine to the medium resulted in synthesis of a radioactive pigment, and tyrosinase activity was demonstrated in extracts of disrupted organisms. Of 15 amino acids added to the medium only tyrosine and tryptophan were used for pigment formation. Pigment production was inhibited by -benzyloxy-phenol, an inhibitor of mammalian melanogenesis. In yeast+ glucose medium a pH range of 6.8-8.2 was optimal for pigment synthesis; more pigment was formed at 20 than at 28 in spite of the fact that there was twice as much growth at the latter temperature. The pigment was precipitated from culture media by a method described for precipitating melanin from urine and in every way tested was identical with a synthetic dihydroxyphenylalanine-melanin. The data indicate that the brown-black pigment synthesized by is melanin.


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