NEUROMELANIN OF THE HUMAN SUBSTANTIA-NIGRA - A MIXED-TYPE MELANIN

Model melanins, synthesized with different cysteinyldopamine/dopamine ratios in the incubates, were oxidized with KMnO4 and the resulting co mpounds were analyzed by HPLC. The ratios between a phaeomelanin-deriv ed compound, thiazole-4,5-dicarboxylic acid (TDCA), and a compound der ived from eumelanin, pyrrole-2,3,5-tricarboxylic acid (PTCA), reflecte d the composition of the model melanins. The neuromelanin of the human substantia nigra was isolated, and the pigment, as well as intact bra in tissue from human substantia nigra was oxidized with KMnO4 and the TDCA/PTCA ratios were determined. Analysis of the isolated neuromelani n showed it to contain 2.3% sulfur and 8.1% nitrogen. The sulfur conte nt indicates the pigment is a mixed-type melanin, and the TDCA/PTCA ra tio indicates that it consists of units derived from benzothiazines an d from indoles in about equal amounts.