Reduction of cytochrome b5 by NADPH-cytochrome P450 reductase
Reduction of cytochrome b5 by NADPH-cytochrome P450 reductase
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DOI：
10.1016/j.abb.2005.06.019
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发表时间：
2005-08-15
影响因子：
3.9
通讯作者：
Guengerich, FP
中科院分区：
文献类型：
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作者：
Guengerich, FP
NADPH-细胞色素P450（P450）还原酶对哺乳动物细胞色素B（5）（B（5））的还原涉及许多生物反应。该过程的动力学以前得到了有限的考虑，并且使用前稳态（停流）和稳态方法的组合来研究B（5）还原的机理。在没有去污剂或脂质的情况下，形成还原酶-b（5）复合物，并缓慢重排为活性形式。在该复合物中，电子向B（5）的转移是迅速的（23 ℃时> 30 s（-1）），与细胞色素c的转移一样快。当存在过量的B（5）时，观察到还原的爆发，这与每个还原酶向一个或两个b5分子的快速电子转移一致，随后发生限速事件。在洗涤剂囊泡中，还原酶和b5迅速相互作用，但电子转移较慢（类似于23 ℃时的3 s（-1））。用二肉豆蔻基卵磷脂囊泡的实验产生了介于非囊泡和洗涤剂系统之间的结果。这些稳态和前稳态动力学提供了在囊泡不存在和存在下还原酶还原b5的不同性质的观点。在没有囊泡的情况下，还原酶和B（5）的相遇是迅速的，随后是初始复合物的缓慢重组（类似于0.07 s（-1）），非常快的还原和解离。在囊泡中，相遇是快速的，而缓慢的步骤（类似于3 s（-1））是在复合物中的还原，与非囊泡系统相比，复合物不利于还原。(c)2005年爱思唯尔公司All rights reserved.
The reduction of mammalian cytochrome b(5) (b(5)) by NADPH-cytochrome P450 (P450) reductase is involved in a number of biological reactions. The kinetics of the process have received limited consideration previously, and a combination of pre-steady-state (stopped-flow) and steady-state approaches was used to investigate the mechanism of b(5) reduction. In the absence of detergent or lipid, a reductase-b(5) complex is formed and rearranges slowly to an active form. Electron transfer to b(5) is rapid within this complex (> 30 s(-1) at 23 degrees C), as fast as to cytochrome c. With excess b(5) present, a burst of reduction is observed, consistent with rapid electron transfer to one or two b5 molecules per reductase, followed by a subsequent rate-limiting event. In detergent vesicles, the reductase and b5 interact rapidly but electron transfer is slower (similar to 3 s(-1) at 23 degrees C). Experiments with dimyristyl lecithin vesicles yielded results intermediate between the non-vesicle and detergent systems. These steady-state and pre- steady-state kinetics provide views of the different natures of the reduction of b5 by the reductase in the absence and presence of vesicles. Without vesicles, the encounter of the reductase and b(5) is rapid, followed by a slow reorganization of the initial complex (similar to 0.07 s(-1)), very fast reduction, and dissociation. In vesicles, encounter is rapid and the slow step (similar to 3 s(-1)) is reduction within a complex less favorable for reduction than in the non-vesicle systems. (c) 2005 Elsevier Inc. All rights reserved.