d'Ischia M, Napolitano A, Prota G
Department of Organic and Biological Chemistry, University of Naples, Italy.
Biochim Biophys Acta. 1991 Mar 4;1073(2):423-30. doi: 10.1016/0304-4165(91)90152-7.
The ability of the peroxidase/H2O2 system to promote the oxidative polymerization of 5,6-dihydroxyindole (DI) and 5,6-dihydroxyindole-2-carboxylic acid (DICA) to melanin pigments was investigated in comparison with tyrosinase. commonly regarded as the sole enzyme involved in melanogenesis. In 0.025 M phosphate buffer at pH 6.8, tyrosinase (2.7 x 10(-3) U/ml) induced a smooth oxidation of 3.0 x 10(-5) M DI (initial rate = 4.4 x 10(-5) M/s) to give a complex mixture of products with the 2,4'-dimer I as the main component, whereas, under the same conditions, peroxidase (0.44 U/ml) and 1.2 x 10(-4) M H2O2 caused the instantaneous conversion of the substrate to a well-defined pattern of products, comprising the 2,4'-and 2,7'-DI dimers I and II, and the related trimers III and IV. When 3.0 x 10(-5) M DICA was used as the substrate, the difference in the effectiveness of the enzymes was much more pronounced. Thus, while peroxidase accomplished the fast oxidation of the indole, yielding the dimer V and the trimer VI as the main products, tyrosinase proved unable to induce more than a poor and sluggish reaction with an initial rate of 5.6.10(-6) M/s. These results raise the possibility that peroxidase, rather than, or in addition to, tyrosinase, may play a critical role in the later stages of the biosynthesis of melanins.
将过氧化物酶/H₂O₂系统促进5,6 - 二羟基吲哚（DI）和5,6 - 二羟基吲哚 - 2 - 羧酸（DICA）氧化聚合成黑色素的能力与酪氨酸酶进行了比较研究。酪氨酸酶通常被认为是黑色素生成中唯一涉及的酶。在pH 6.8的0.025 M磷酸盐缓冲液中，酪氨酸酶（2.7×10⁻³ U/ml）诱导3.0×10⁻⁵ M DI平稳氧化（初始速率 = 4.4×10⁻⁵ M/s），生成以2,4'-二聚体I为主要成分的复杂产物混合物，而在相同条件下，过氧化物酶（0.44 U/ml）和1.2×10⁻⁴ M H₂O₂导致底物瞬间转化为明确的产物模式，包括2,4'-和2,7'-DI二聚体I和II以及相关的三聚体III和IV。当使用3.0×10⁻⁵ M DICA作为底物时，酶的有效性差异更为明显。因此，虽然过氧化物酶完成了吲哚的快速氧化，产生二聚体V和三聚体VI作为主要产物，但酪氨酸酶证明只能诱导一个缓慢且反应不佳的反应，初始速率为5.6×10⁻⁶ M/s。这些结果增加了一种可能性，即过氧化物酶可能在黑色素生物合成的后期阶段发挥关键作用，而非酪氨酸酶，或者是除酪氨酸酶之外发挥关键作用。
