Cytochrome cd1, reductive activation and kinetic analysis of a multifunctional respiratory enzyme
Cytochrome cd1, reductive activation and kinetic analysis of a multifunctional respiratory enzyme
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DOI：
10.1074/jbc.m108944200
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发表时间：
2002-02-01
影响因子：
4.8
通讯作者：
Ferguson, SJ
中科院分区：
文献类型：
--
作者：
Richter, CD;Allen, JWA;Ferguson, SJ
泛养副球菌细胞色素cd（1）是一种细菌呼吸酶，在体内能利用亚硝酸盐，在体外也能利用羟胺和氧作为电子受体。我们提出了一个全面的分析，每个电子受体和三个电子供体，pseudoazurin和细胞色素c（550），生理和非生理马心细胞色素c的酶的稳态动力学特性。在pH值为5.8时，最适合于亚硝酸盐还原，该酶的周转数高达121 s（-1）/d（1）血红素，显著高于以前观察到的任何细胞色素cd（1）。通过还原预活化酶是建立与任何电子供体蛋白质的完全催化能力所必需的。在任何方面，替代生理电子供体之间没有显著的动力学差异，这为假特异性的概念提供了支持，其中具有实质上不同的三级结构的蛋白质可以将电子转移到相同的受体。还报道了低水平的羟胺还原酶活性，这可能是细胞色素c的固有性质。根据最近快速反应研究中的新观察结果，讨论了泛养毕赤酵母细胞色素cd（1）酶学的重要意义，并提出了关于亚硝酸盐还原机制的建议。
Paracoccus pantotrophus cytochrome cd(1) is an enzyme of bacterial respiration, capable of using nitrite in vivo and also hydroxylamine and oxygen in vitro as electron acceptors. We present a comprehensive analysis of the steady state kinetic properties of the enzyme with each electron acceptor and three electron donors, pseudoazurin and cytochrome c(550), both physiological, and the non-physiological horse heart cytochrome c. At pH 5.8, optimal for nitrite reduction, the enzyme has a turnover number up to 121 s(-1) per d(1) heme, significantly higher than previously observed for any cytochrome cd(1). Pre-activation of the enzyme via reduction is necessary to establish full catalytic competence with any of the electron donor proteins. There is no significant kinetic distinction between the alternative physiological electron donors in any respect, providing support for the concept of pseudospecificity, in which proteins with substantially different tertiary structures can transfer electrons to the same acceptor. A low level hydroxylamine disproportionase activity that may be an intrinsic property of cytochromes c is also reported. Important implications for the enzymology of P. pantotrophus cytochrome cd(1) are discussed and proposals are made about the mechanism of reduction of nitrite, based on new observations placed in the context of recent rapid reaction studies.