Körner A, Pawelek J
Science. 1982 Sep 17;217(4565):1163-5. doi: 10.1126/science.6810464.
The biosynthesis of melanin is initiated by the catalytic oxidation of tyrosine to dopa by tyrosinase in a reaction that requires dopa as a cofactor. Tyrosine then catalyzes the dehydrogenation of dopa to dopaquinone. The subsequent reactions can proceed spontaneously in vitro. Tyrosinase, purified from murine melanomas and the skins of brown mice, has now been shown to catalyze a third reaction in mammalian melanogenesis, namely the conversion of 5,6-dihydroxyindile to melanochrome. This reaction requires dopa as a cofactor and is inhibited by tyrosine. Conversely, 5,6-dihydroxyindole inhibits the oxidation of tyrosine to dopa, so that the relative concentrations of tyrosine and 5,6-dihydroxyindole within the mammalian pigment cell are capable of regulating melanogenesis in a previously unrecognized fashion. Tyrosinase has the unusual property of catalyzing three distinct reactions within a single biochemical pathway: the hydroxylation of a monophenol, the dehydrogenation of a catechol, and the dehydrogenation of a dihydroxyindole. The first and third of these reactions require dopa as a cofactor; in the second reaction, dopa is a substrate.
黑色素的生物合成始于酪氨酸酶将酪氨酸催化氧化为多巴的反应，该反应需要多巴作为辅助因子。然后酪氨酸催化多巴脱氢生成多巴醌。后续反应在体外可自发进行。从鼠黑色素瘤和棕色小鼠皮肤中纯化得到的酪氨酸酶，现已证明它在哺乳动物黑色素生成过程中催化第三个反应，即将5,6 -二羟基吲哚转化为黑素chrome。该反应需要多巴作为辅助因子，并受到酪氨酸的抑制。相反，5,6 -二羟基吲哚抑制酪氨酸氧化为多巴，因此哺乳动物色素细胞内酪氨酸和5,6 -二羟基吲哚的相对浓度能够以一种前所未有的方式调节黑色素生成。酪氨酸酶具有在单一生化途径中催化三种不同反应的独特特性：单酚的羟基化、儿茶酚的脱氢以及二羟基吲哚的脱氢。这些反应中的第一个和第三个需要多巴作为辅助因子；在第二个反应中，多巴是底物。
