The peroxidase activity of cytochrome c-550 from Paracoccus versutus
The peroxidase activity of cytochrome c-550 from Paracoccus versutus
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DOI：
10.1046/j.1432-1327.2001.02335.x
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发表时间：
2001-08-01
期刊：
影响因子：
--
通讯作者：
Canters, GW
中科院分区：
文献类型：
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作者：
Diederix, REM;Ubbink, M;Canters, GW
除了它们的天然电子传递能力，c型细胞色素在过氧化氢存在下具有低过氧化物酶和细胞色素P-450活性。这些催化性质，结合它们的结构稳健性和共价结合的辅因子，使细胞色素成为潜在有用的过氧化物酶模拟物。本研究报告的过氧化物酶活性的细胞色素c-550从副球菌versutus和这种活性的损失，在过氧化氢的存在下。细胞色素c-550的过氧化物酶反应中的速率决定步骤是在过氧化物与血红素铁结合之后形成反应性中间体。与辣根过氧化物酶（约百万分之一）相比，反应速率非常低，因为血红素铁对H2 O2的可及性差，并且缺乏碱催化剂，例如过氧化物酶的远端His。这通过反应速率对过氧化物浓度的线性依赖性得到证实，该过氧化物浓度高达至少1 M H2 O2。还原底物愈创木酚的稳态转化之前是活化阶段，这归因于蛋白质上氨基酸自由基的积累。在不存在还原性底物的情况下的失活动力学是单指数的，并且显示出与血红素降解至25 mm H2 O2（pH 8.0）同时发生。在更高的过氧化物浓度，失活动力学是双相的，作为一个显着的保护作用的H2 O2的结果，涉及超氧化物和亚铁细胞色素c-550的形成。
Next to their natural electron transport capacities, c-type cytochromes possess low peroxidase and cytochrome P-450 activities in the presence of hydrogen peroxide. These catalytic properties, in combination with their structural robustness and covalently bound cofactor make cytochromes c potentially useful peroxidase mimics. This study reports on the peroxidase activity of cytochrome c-550 from Paracoccus versutus and the loss of this activity in presence of H2O2. The rate-determining step in the peroxidase reaction of cytochrome c-550 is the formation of a reactive intermediate, following binding of peroxide to the haem iron. The reaction rate is very low compared to horseradish peroxidase (approximately one millionth), because of the poor accessibility of the haem iron for H2O2, and the lack of a base catalyst such as the distal His of the peroxidases. This is corroborated by the linear dependence of the reaction rate on the peroxide concentration up to at least 1 M H2O2. Steady-state conversion of a reducing substrate, guaiacol, is preceded by an activation phase, which is ascribed to the build-up of amino-acid radicals on the protein. The inactivation kinetics in the absence of reducing substrate are mono-exponential and shown to be concurrent with haem degradation up to 25 mm H2O2 (pH 8.0). At still higher peroxide concentrations, inactivation kinetics are biphasic, as a result of a remarkable protective effect of H2O2, involving the formation of superoxide and ferrocytochrome c-550.