SUPEROXIDE DISMUTASE - COMPARISON OF RATE CONSTANTS
SUPEROXIDE DISMUTASE - COMPARISON OF RATE CONSTANTS
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DOI：
10.1016/0003-9861(73)90636-x
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发表时间：
1973-01-01
影响因子：
3.9
通讯作者：
FRIDOVICH, I
中科院分区：
文献类型：
--
作者：
FORMAN, HJ;FRIDOVICH, I
O2-以恒定速率引入缓冲水溶液中，或者通过机械注入溶解在四氢呋喃中的KO 2，或者通过黄嘌呤氧化酶对黄嘌呤加氧的原位作用。使该O2-与ferricytochromecor和四硝基甲烷反应，并分别通过电化学方法监测反应产物ferrocytochromecor nitroforms的形成。测定了超氧化物歧化酶的浓度，该浓度与给定水平的细胞色素或四硝基甲烷竞争，从而导致对硝基仿的铁细胞色素积累速率的50%抑制。根据已知的O2-与铁细胞色素和四硝基甲烷反应的速率常数，计算出牛红细胞中含铜和锌的酶对O2-的酶促歧化反应的速率常数，发现在pH 7.8和8.5时为2 × 109 m − 1 sec − 1。该速率常数是在10− 8 m → 10− 13 m范围内O2−浓度处于稳态时获得的，与在10− 5 m范围内O2−浓度进行的脉冲辐解研究结果完全一致。因此，在10−5→ 10− 13 m范围内，O2−的酶歧化反应的二级速率常数与O2−的浓度无关。这些酶包括大肠杆菌的锰酶和鸡肝线粒体的锰酶以及弗罗姆的铁酶。杆菌还研究了这些酶催化的歧化反应的速率常数随pH的变化。
O2−was introduced, at a constant rate, into buffered aqueous solutions, either by mechanical infusion of KO2, dissolved in tetrahydrofuran, or by thein situaction of xanthine oxidase on xanthine plus oxygen. This O2−was allowed to react with ferricytochromecor with tetranitromethane and the formation of the reaction products, ferrocytochromecor nitroform, respectively, was monitored spectrophotometrically. That concentration of Superoxide dismutase, which competed equally with given levels of cytochromecor tetranitromethane and which thus caused 50% inhibition of the rates of accumulation of ferrocytochromecor of nitroform, was determined. The rate constant for the enzymatic dismutation of O2−by the copper and zinc containing enzyme from bovine erythrocytes was then calculated from the known rate constants for the reaction of O2−with ferricytochromecand with tetranitromethane and was found to be 2 × 109m−1sec−1at pH 7.8 and 8.5. This rate constant was obtained at steady-state concentrations of O2−in the 10−8m→ 10−13mrange and is in full agreement with the results of pulse radiolytic investigations which were performed at O2−concentrations in the 10−5mrange. The second order rate constant for the enzymatic dismutation of O2−is thus independent of the concentration of O2−in the range 10−5→ 10−13m.Several distinct types of Superoxide dismutase have been described. These include the mangano-enzymes fromEscherichia coliand from chicken liver mitochondria and the iron-enzyme fromE. coli. The rate constants for the dismutations catalyzed by these enzymes have also been investigated as a function of pH.