A comparative study of the physical and chemical properties of melanins isolated from human black and red hair

Abstract

Some of the physical and chemical properties of the melanins isolated from human black and red hair were compared. Some of these properties were also compared with those of synthetic dopa melanin. Five samples each of black and red hair were used for isolating melanin by extraction with 2.5 M NaOH, and purification by repeated precipitation with HCl and redissolution in NaOH. The proteins associated with the melanins were hydrolyzed by refluxing the melanoproteins in 6 M HCl. The melanoproteins from black and red hair had 55.8 ± 2.0% and 41.5 ± 2.5% melanin, respectively. There was no statistically significant difference between the amino acid compositions of the hydrolysates from black and red hair melanoproteins. The ultraviolet and visible spectra of red hair melanin showed significant differences from those of black hair melanin and dopa melanin. Even though the overall spectra of red hair melanin showed some differences from those of black hair and dopa melanins, the results indicate a close similarity in the groups identifiable by the IR spectra. The compositions of C, H, N, S, and O in these melanins were determined. Red hair melanin contained more S than black hair melanin; dopa melanin did not contain any S. Black and red hair melanins oxidized NADH at approximately the same rate. Ultraviolet irradiation increased the oxidation of NADH by red hair melanin to a greater extent than that by black hair melanin. These results show that although there are general similarities, there are significant differences in the physical and chemical properties of melanins isolated from black and red hair.