Studies on melanogenesis of tryptophan in Harding-Passey mouse melanoma

D,L-tryptophan[benzene ring-14C (U)] and D,L-tryptophan (methylene-14C) are incorporated significantly into melanin of Harding-Passey mouse melanoma. D,L-5-hydroxytryptophan (methylene-14C) and 5-hydroxytryptamine-3-14C (serotonin) gave an incorporation of radioactivity into melanin significantly lower than tryptophan. D,L-tyrosine-2-14C was incorporated into melanin as well as tryptophan. Therefore tryptophan must be considered an important precursor in the biogenesis of melanins too.