MELANINS IN IGR-1 MELANOMA-CELLS

Information on the composition of melanins is obtained by analysis bot h of 4-amino-3-hydroxyphenylalanine (AHP) after hydriodic acid degrada tion and of pyrrole-2,3,5-tricarboxylic acid (PTCA) after potassium pe rmanganate oxidation. Analysis of thiazole-4,5-dicarboxylic acid (TDCA ) and pyrrole-2,3-dicarboxylic acid (PDCA) after permanganate oxidatio n, provides additional information on the composition, TDCA on pheomel anin residues, and PDCA on indolic residues without carboxy groups. Us ing model melanins formed from dopa and cysteinyldopa in different pro portions, we found the TDCA/(PTCA+PDCA) ratio to yield a reliable esti mate of the relative proportions of pheomelanin and eumelanin. The PDC A/PTCA ratio reflects the relationship between indole residues with an d without carboxy groups. We have analyzed degradation products from c ultures of IGR 1, an extensively studied melanoma cell line. Cell cult ures were harvested after 2, 4, and 7 days. Culture media were changed after 2 days in all series, and also after 4 days in one series harve sted at 7 days. Cells without medium change had seven times the amount of melanin found in cultures with medium change. The PDCA/PTCA ratio decreased with increasing amounts of melanin. With increased melanizat ion, eumelanin is increased relatively more than pheomelanin. The cell content of 5-S-cysteinyldopa (5-S-CD) was similar in all cultures, wh ile 6-hydroxy-5-methoxyindole-2-carboxylic acid (6H5MICA), a eumelanin precursor metabolite, was found in increased amounts of media of heav ily pigmented cultures.