Agrup G, Rorsman H, Rosengren E
Acta Derm Venereol. 1982;62(5):371-76.
The formation of 5-OH-dopa on incubation of tyrosine or dopa with mushroom tyrosinase was studied. Dopa oxidase activity was defined by measuring the formation of 5-S- and 2-S-cysteinyldopa from dopa in the presence of excess amounts of cysteine. This procedure quantitating the immediate nucleophilic reaction products of dopaquinone constitutes a new method for assessing tyrosinase activity. The rate of 5-OH-dopa formation from dopa was similar to that of the formation of dopa from tyrosine. The rate of dopaquinone formation was one order of magnitude higher. When tyrosine was oxidized in the presence of ascorbic acid, 5-OH-dopa formation represented 14% of the original amount of tyrosine. At low concentration of dopa, formation of 5-OH-dopa was proportional to the dopa concentration. At high concentrations the relative quantity of 5-OH-dopa formed decreased. Tyrosine in high concentrations inhibited the formation of 5-OH-dopa from dopa. 5-OH-dopa proved to be a substrate for tyrosinase. The rate of oxidation of 5-OH-dopa was similar to that of dopa. The oxidation products of 5-OH-dopa were transformed into relatively stable fluorophores.
研究了酪氨酸或多巴与蘑菇酪氨酸酶温育时5-羟基多巴的形成。多巴氧化酶活性通过在过量半胱氨酸存在下测量多巴生成5-S-和2-S-半胱氨酰多巴来定义。这种对多巴醌的直接亲核反应产物进行定量的方法构成了一种评估酪氨酸酶活性的新方法。多巴生成5-羟基多巴的速率与酪氨酸生成多巴的速率相似。多巴醌的生成速率高一个数量级。当酪氨酸在抗坏血酸存在下被氧化时，5-羟基多巴的生成量占酪氨酸原始量的14%。在低浓度多巴时，5-羟基多巴的生成与多巴浓度成正比。在高浓度时，生成的5-羟基多巴的相对量减少。高浓度的酪氨酸抑制多巴生成5-羟基多巴。事实证明5-羟基多巴是酪氨酸酶的一种底物。5-羟基多巴的氧化速率与多巴相似。5-羟基多巴的氧化产物转化为相对稳定的荧光团。
