The chemical characterization of melanin contained in substantia nigra of human brain.

The pigment of substantia nigra human brain has been extracted by a mild procedure consisting of washes with phosphate buffer, methanol and incubation with SDS-proteinase. Pyrolysis gas chromatography mass spectrometry, infrared spectrometry, termogravimetric analysis and elemental analysis were the techniques used for the chemical characterization. An indole moiety bound to a sulfur containing amino acid and to palmitic acid were the main aspects found in the structure. The presence of a 7% inorganic component was observed. This probably contains Fe, Cu, Zn and Cr which are also relevant, for the formation and the role of melanin in substantia nigra neurons. The fatty acid moiety is chemically bound to the indole structure as it was not eliminated by repeated methanol washing. The same situation occurs for the sulfur containing group. Considering these data and the most abundant molecules present in substantia nigra the precursor of neuromelanin seems to be a cysteinyl-catechol, to which is then bound a palmityl group.