Jacobsohn G M, Jacobsohn M K
Arch Biochem Biophys. 1984 Jul;232(1):189-96. doi: 10.1016/0003-9861(84)90534-4.
The hydroxylating activity of mushroom tyrosinase has been utilized for over a decade in the preparation of 2-hydroxyestradiol from estradiol, yet this same enzyme is known to function as an oxidant of o-dihydric compounds to the corresponding o-quinones. It was questioned why catechol estrogens do not react further, particularly since the tyrosinase activity (hydroxylating) is exceeded many fold by the diphenol oxidase activity of the enzyme. This report describes that the catechol estrogen will react in presence of enzyme but only if catechol is also present. Diphenol oxidase activity was measured either by the polarographic oxygen-utilization technique or by changes in the absorption spectrum at 206 and 256 nm. The enzyme activity was standardized with catechol (Km = 5.2 X 10(-4) M). The steroid did not react with the enzyme if catechol was absent. With catechol, the steroid reacted rapidly and completely (Km = 4.2 X 10(-4) M). The consumption of oxygen with catechol and 2-hydroxyestradiol was additive and stoichiometric, 1 g-atom oxygen/mol of either substrate. Kinetic analysis shows that catechol functions as an activator of the tyrosinase.
十多年来，蘑菇酪氨酸酶的羟化活性一直被用于从雌二醇制备2-羟基雌二醇，然而，人们已知这种酶可作为邻二羟基化合物氧化为相应邻醌的氧化剂。有人质疑为什么儿茶酚雌激素不会进一步反应，特别是因为该酶的二酚氧化酶活性比酪氨酸酶活性（羟化）高出许多倍。本报告描述了儿茶酚雌激素在酶存在的情况下会发生反应，但前提是儿茶酚也存在。二酚氧化酶活性通过极谱氧利用技术或206和256nm处吸收光谱的变化来测量。酶活性用儿茶酚（Km = 5.2×10^(-4) M）进行标准化。如果没有儿茶酚，该类固醇不会与酶发生反应。有儿茶酚时，该类固醇会迅速且完全反应（Km = 4.2×10^(-4) M）。儿茶酚和2-羟基雌二醇的耗氧量是相加的且符合化学计量关系，即每摩尔任何一种底物消耗1克原子氧。动力学分析表明儿茶酚作为酪氨酸酶的激活剂起作用。
