SYNTHESIS AND CHARACTERIZATION OF MELANINS FROM DIHYDROXYINDOLE-2-CARBOXYLIC ACID AND DIHYDROXYINDOLE

被引:79
作者
ORLOW, SJ
OSBER, MP
PAWELEK, JM
机构
[1] YALE UNIV,SCH MED,DEPT DERMATOL,NEW HAVEN,CT 06510
[2] YALE UNIV,SCH MED,DEPT PHARMACOL,NEW HAVEN,CT 06510
[3] NYU MED CTR,DEPT DERMATOL,NEW YORK,NY 10016
[4] NYU MED CTR,DEPT CELL BIOL,NEW YORK,NY 10016
来源
PIGMENT CELL RESEARCH | 1992年 / 5卷 / 03期
关键词
SOLUBLE MELANINS; DOPACHROME TAUTOMERASE; BROWN PIGMENTS;
D O I
10.1111/j.1600-0749.1992.tb00007.x
中图分类号
Q2 [细胞生物学];
学科分类号
071009 ; 090102 ;
摘要
Several studies have confirmed that a melanocyte-specific enzyme, dopachrome tautomerase (EC 5.3.2.3), catalyzes the isomerization of dopachrome to 5,6-dihydroxyindole-2-carboxylic acid (DHICA) (Pawelek, 1991). Here we report that DHICA, produced either enzymatically with dopachrome tautomerase or through chemical synthesis, spontaneously polymerized to form brown melanin that was soluble in aqueous solutions above pH 5. Under the same reaction conditions, solutions of either DOPA, DOPAchrome, or 5,6-dihydroxyindole (DHI) formed black, insoluble melanin precipitates. When DHICA and DHI were mixed together, with DHICA in molar excess, little or no precipitation of DHI-melanin occurred and the rate and extent of soluble melanin formation was markedly enhanced over that achieved with DHICA alone, suggesting co-polymerization of DHICA and DHI. With or without DHI, DHICA-melanins absorbed throughout the ultraviolet and visible spectra (200-600 nm). The DHICA-melanins precipitated below pH 5, at least in part because of protonation of the carboxyl groups. DHICA-melanins could be passed through 0.22-mu-m filters but could not be dialyzed through semi-permeable membranes with exclusion limits of 12,000-14,000 daltons. HPLC/molecular sieve analyses revealed apparent molecular weights ranging from 20,000 to 200,000 daltons, corresponding to 100-1,000 DHICA monomers per molecule of melanin. DHICA-melanins were stable to boiling, lyophilization, freezing and thawing, and incubation at room temperature for more than 1 year. The natural occurrence of oligomers of DHICA was first reported by Ito and Nichol (1974) in their studies of the brown tapetal pigment in the eye of the sea catfish (Arius felis L.). In experiments reported here, brown, but not black, melanins from mouse hairs, human melanoma cells, and peacock feathers were soluble in aqueous buffers. Since DHICA-melanins are both soluble and brown, the results raise the possibility that they are determinants of brown colors in the animal kingdom.
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页码:113 / 121
页数:9
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