Protein conformational perturbations affect the photoreduction of native cytochrome c peroxidase (III) at alkaline pH.
Protein conformational perturbations affect the photoreduction of native cytochrome c peroxidase (III) at alkaline pH.
复制标题
蛋白质构象扰动会影响天然细胞色素 c 过氧化物酶 (III) 在碱性 pH 下的光还原。
DOI：
10.1021/bi00166a020
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发表时间：
1992
期刊：
影响因子：
2.9
通讯作者：
Ondrias,MR
中科院分区：
文献类型：
--
作者：
Wang,J;Zhu,H;Ondrias,MR
修订稿于 1992 年 10 月 14 日收到摘要：当在 7.30-9.70 的 pH 范围内滴定时，三价铁细胞色素 c 过氧化物酶 (CCP) 经历从五配位、高自旋 (5c/hs) 血红素到六配位、低自旋 (6c/Is) 血红素的连接状态转变。这种行为类似于酶的亚铁形式所表现出的行为。然而，在碱性 pH 值下，亚铁 CCP 表现出低自旋轴向配体的光解离，但在三价 CCP 中未观察到。相反，在 7.90-9.70 的 pH 范围内，光诱导的铁血红素还原是明显的。在缺乏O 2 氧化还原介质例如甲基紫精(MV2+)的情况下，光还原酶的再氧化非常慢(/2～3分钟)。 F~ 结合的 CCP (III)(6c/hs) 表现出类似的 pH 依赖性光还原作用。然而，辣根过氧化物酶则不然。 6c/Is 血红素的形成与 CCP (III) 在碱性 pH 下明显光还原（激光脉冲之间，> 60 ms）的开始一致，表明其血红素袋内或周围存在整体蛋白质构象重排。碱性 CCP (III) 的光还原很可能涉及从近端血红素袋中的芳香族残基到光激发血红素的分子内电子转移 (ET)。我们推测电子转移动力学受到 Trp-191 方向变化的影响。
Revised Manuscript Received October 14, 1992 abstract: Ferric cytochrome c peroxidase (CCP) undergoes a ligation-state transition from a pentaco-ordinate, high-spin (5c/hs) heme to a hexacoordinate, low-spin (6c/Is) heme when titrated over a pH range of 7.30-9.70. This behavior is similar to that exhibited bythe ferrousform of the enzyme. However, the photodissociation of the low-spin, axial ligand, exhibited by ferrous CCP at alkaline pH, is not observed for ferric CCP. Instead, a photoinduced reduction of the ferric heme is apparent in the pH range 7.90-9.70. In the absence of 02 andredox mediators such as methyl viologen (MV2+), the reoxidation of the photoreduced enzyme is very slow (/2~ 3 min). F~-bound CCP (III)(6c/hs) displays similar pH-dependent photoreduction. Horseradish peroxidase, however, does not. Theformation of 6c/Is heme coincides with the onset of appreciable photoreduction (between laser pulses,> 60 ms) of CCP (III) at alkalinepH, suggesting a global protein conformational rearrangement within or around its heme pocket. Photoreduction of alkaline CCP (III) most likely involves intramolecular electron transfer (ET) from the aromatic residue in the proximal heme pocket to the photoexcited heme. We speculate that the kinetics of electron transfer are affected bychanges in the orientation of Trp-191.