Chemical characterization of eumelanins with special emphasis on 5,6-dihydroxyindole-2-carboxylic acid content and molecular size.
Mammalian melanins exist in two chemically distinct forms; the brown to black eumelanins and the yellow to reddish pheomelanins. Eumelanins are derived from copolymerization of 5,6-dihydroxyindole (DHI) and 5,6-dihydroxyindole-2-carboxylic acid (DHICA). Eumelanins can be quantified by HPLC analysis of the oxidation product pyrrole-2,3,5-tricarboxylic acid (PTCA) and by our spectrophotometric method (Sp.EM). We also developed a spectrophotometric method for assaying the total amount of eu- and pheomelanins by dissolving them in Soluene-350 (TM). In addition, we previously showed that Sp.EM/TM and PTCA/TM ratios are significant parameters in characterizing eumelanins produced in follicular melanocytes. The objectives of this study were (1) to clarify the significance of Sp.EM/TM and PTCA/TM ratios in synthetic eumelanins and (2) to apply these methods to characterizing natural eumelanins with various DHI/ DHICA ratios and molecular sizes. The results obtained show that (1) the Sp.EM/TM ratio of synthetic eumelanins increases as polymerization proceeds, (2) the Sp.EM/TM and PTCA/TM ratios in copolymers of DHI and DHICA correlate to the percentage content of DHICA-derived units, and (3) combination of the Sp.EM/TM and PTCA/TM ratios serves to estimate the DHICA content and the degree of polymerization in natural eumelanins.
Ozeki
H
H
School of Medicine, Fujita Health University, Aichi, Japan.
Wakamatsu
K
K
Ito
S
S
Ishiguro
I
I
D000818:Animals; D004295:Dihydroxyphenylalanine / Q000737:chemistry; D006801:Humans; D007211:Indoles / Q000032:analysis*; D008543:Melanins / Q000737:chemistry*; D051379:Mice; D008970:Molecular Weight; D011108:Polymers; D011758:Pyrroles / Q000032:analysis*; D000644:Quaternary Ammonium Compounds; D012997:Solvents; D013053:Spectrophotometry / Q000379:methods*; D014443:Tyrosine / Q000737:chemistry
D007211:Indoles; D008543:Melanins; D011108:Polymers; D011758:Pyrroles; D000644:Quaternary Ammonium Compounds; D012997:Solvents; C041877:eumelanin; C002982:Soluene; D014443:Tyrosine; C030692:5,6-dihydroxy-2-indolylcarboxylic acid; D004295:Dihydroxyphenylalanine; C071226:pyrrole-2,3,5-tricarboxylic acid; C033871:5,6-dihydroxyindole