Lindbladh C, Rorsman H, Rosengren E
Acta Derm Venereol. 1983;63(3):209-14.
When tyrosine was incubated with tyrosinase in the presence of ascorbic acid, dopa and 5-hydroxydopa were formed and the enzyme was inactivated. In the presence of catalase, more dopa and 5-hydroxydopa were formed because enzyme inactivation was prevented. Incubation of dopa and cysteine with small amounts of mushroom tyrosinase led to rapid inactivation of the enzyme. This inactivation was accelerated in the presence of catalase. New systems developed have been useful in demonstrating the role of hydrogen peroxide in tyrosinase inactivation by several compounds of importance in melanin biochemistry. Cysteine and glutathione inactivated tyrosinase. Addition of catalase increased the inactivation at high thiol concentrations, but decreased the inactivation at low concentrations. Ascorbic acid and 5-hydroxydopamine also inactivated tyrosinase, but with these compounds inactivation was completely prevented by addition of catalase. The inactivation by dopamine was negligible under the experimental conditions. Inactivation of tyrosinase by ascorbic acid and by 5-OH-dopamine was found dependent on oxygen, whereas inactivation by cysteine and glutathione was independent of oxygen. Large amounts of serum albumin protected tyrosinase from inactivation by ascorbic acid and 5-OH-dopamine, but did not prevent inactivation by cysteine and glutathione. The presence of substrate had a protective effect on the inactivation of tyrosinase by cysteine.
当酪氨酸在抗坏血酸存在的情况下与酪氨酸酶一起温育时，会形成多巴和5-羟基多巴，并且该酶会失活。在过氧化氢酶存在的情况下，会形成更多的多巴和5-羟基多巴，因为酶的失活被阻止了。将多巴和半胱氨酸与少量蘑菇酪氨酸酶一起温育会导致该酶迅速失活。在过氧化氢酶存在的情况下，这种失活会加速。新开发的系统已有助于证明过氧化氢在酪氨酸酶被黑色素生物化学中几种重要化合物失活过程中的作用。半胱氨酸和谷胱甘肽会使酪氨酸酶失活。添加过氧化氢酶在高硫醇浓度下会增加失活，但在低浓度下会降低失活。抗坏血酸和5-羟基多巴胺也会使酪氨酸酶失活，但对于这些化合物，添加过氧化氢酶可完全阻止失活。在实验条件下，多巴胺的失活可忽略不计。发现抗坏血酸和5-羟基多巴胺对酪氨酸酶的失活取决于氧气，而半胱氨酸和谷胱甘肽引起的失活与氧气无关。大量血清白蛋白可保护酪氨酸酶不被抗坏血酸和5-羟基多巴胺失活，但不能阻止半胱氨酸和谷胱甘肽引起的失活。底物的存在对半胱氨酸使酪氨酸酶失活具有保护作用。
