Smit N, Tilgmann C, Karhunen T, Slingerland R, Ulmanen I, Westerhof W, Pavel S
Department of Dermatology, Academic Medical Center, Amsterdam, The Netherlands.
Pigment Cell Res. 1994 Dec;7(6):403-8. doi: 10.1111/j.1600-0749.1994.tb00069.x.
O-Methylation of L-dopa was investigated as a possible regulatory mechanism in melanin metabolism. The methylation product of L-dopa, 3-O-methoxytyrosine was detected in extracts of cultured human melanocytes. The enzyme catechol-O-methyltransferase is responsible for this O-methylation and that of the dihydroxyindolic intermediates of melanogenesis. The enzyme is present in melanocytes in its soluble and membrane-bound isoforms. Immuno-electron microscopy suggests the presence of the membrane-bound enzyme in the endoplasmic reticulum. This localization may indicate a role of catechol-O-methyltransferase in protecting the melanocyte against reactive dihydroxyphenolic intermediates of melanogenesis leaking from the melanogenic compartments. On the other hand, the O-methylation of L-dopa may serve as a regulatory point in melanogenesis during early stage of tyrosinase processing in the endoplasmic reticulum.
左旋多巴的O-甲基化作为黑色素代谢中一种可能的调节机制进行了研究。在培养的人黑素细胞提取物中检测到左旋多巴的甲基化产物3-O-甲氧基酪氨酸。儿茶酚-O-甲基转移酶负责这种O-甲基化以及黑色素生成的二羟基吲哚中间体的O-甲基化。该酶以其可溶性和膜结合同工型存在于黑素细胞中。免疫电子显微镜显示内质网中存在膜结合酶。这种定位可能表明儿茶酚-O-甲基转移酶在保护黑素细胞免受从黑素生成区室泄漏的黑色素生成反应性二羟基酚中间体的作用。另一方面，左旋多巴的O-甲基化可能在内质网中酪氨酸酶加工的早期阶段作为黑色素生成的调节点。
