The reactions of heme- and verdoheme-heme oxygenase-1 complexes with FMN-depleted NADPH-cytochrome P450 reductase - Electrons required for verdoheme oxidation can be transferred through a pathway not involving FMN
The reactions of heme- and verdoheme-heme oxygenase-1 complexes with FMN-depleted NADPH-cytochrome P450 reductase - Electrons required for verdoheme oxidation can be transferred through a pathway not involving FMN
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DOI：
10.1074/jbc.m606163200
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发表时间：
2006-10-20
影响因子：
4.8
通讯作者：
Noguchi, Masato
中科院分区：
文献类型：
--
作者：
Higashimoto, Yuichiro;Sato, Hideaki;Noguchi, Masato
血红素加氧酶(HO)反应中利用的电子由NADPH-细胞色素P450还原酶(CPR)提供。为了研究CPR到HO的电子传递途径，我们用大鼠去FMN的CPR研究了血红素降解的第二中间体--血红素和马鞭铁血红素与大鼠HO-1(RHO-1)的反应，通过透析CPR突变体Y140A/Y178A对抗2M KBR制备了去FMN的CPR。尽管FMN缺失的CPR能够与血红素-Rho-1复合体结合，但与Rho-1的结合亲和力与野生型CPR相当，但FMN缺失的CPR没有发生血红素的降解。因此，与Rho-1络合的血红素铁还原的第一个电子必须从FMN转移。相反，马鞭铁在去FMN的CPR中被转化为胆绿素铁络合物，这种转化被铁氰化物抑制，这表明电子是马鞭铁转化为胆绿素铁络合物所必需的，它们可以通过一条不涉及FMN的途径，可能通过FAD提供给去FMN的CPR。观察到铁原卟啉IX二甲酯-Rho-1络合物与野生型CPR反应中积累了马鞭草素二甲酯，支持了这一结论。通过加入野生型CPR或去铁胺，将FMN耗尽的CPR生成的胆绿素铁络合物转化为胆绿素。
Electrons utilized in the heme oxygenase (HO) reaction are provided by NADPH-cytochrome P450 reductase (CPR). To investigate the electron transfer pathway from CPR to HO, we examined the reactions of heme and verdoheme, the second intermediate in the heme degradation, complexed with rat HO-1 (rHO-1) using a rat FMN-depleted CPR; the FMN-depleted CPR was prepared by dialyzing the CPR mutant, Y140A/Y178A, against 2 M KBr. Degradation of heme in complex with rHO-1 did not occur with FMN-depleted CPR, notwithstanding that the FMN-depleted CPR was able to associate with the heme-rHO-1 complex with a binding affinity comparable with that of the wild-type CPR. Thus, the first electron to reduce the ferric iron of heme complexed with rHO-1 must be transferred from FMN. In contrast, verdoheme was converted to the ferric biliverdin-iron chelate with FMN-depleted CPR, and this conversion was inhibited by ferricyanide, indicating that electrons are certainly required for conversion of verdoheme to a ferric biliverdin-iron chelate and that they can be supplied from the FMN-depleted CPR through a pathway not involving FMN, probably via FAD. This conclusion was supported by the observation that verdoheme dimethyl esters were accumulated in the reaction of the ferriprotoporphyrin IX dimethyl ester-rHO-1 complex with the wild-type CPR. Ferric biliverdin-iron chelate, generated with the FMN-depleted CPR, was converted to biliverdin by the addition of the wild-type CPR or desferrioxamine.