METHENE BRIDGE CARBON-ATOM ELIMINATION IN OXIDATIVE HEME DEGRADATION CATALYZED BY HEME OXYGENASE AND NADPH-CYTOCHROME-P-450 REDUCTASE
METHENE BRIDGE CARBON-ATOM ELIMINATION IN OXIDATIVE HEME DEGRADATION CATALYZED BY HEME OXYGENASE AND NADPH-CYTOCHROME-P-450 REDUCTASE
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DOI：
10.1016/0003-9861(84)90241-8
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发表时间：
1984-01-01
影响因子：
3.9
通讯作者：
SCHACTER, BA
中科院分区：
文献类型：
--
作者：
DOCHERTY, JC;FIRNEISZ, GD;SCHACTER, BA
生理血红素降解是由血红素加氧酶系统介导的，该系统由血红素加氧酶和NADPH-细胞色素P-450还原酶组成。胆绿素 IX.alpha。通过消除一个亚甲基桥 C 原子形成 CO。单独纯化的 NADPH-细胞色素 P-450 还原酶也会降解血红素，但胆绿素是次要产物 (15%)。通过分析 [14C] 血红素降解中 14CO 的回收情况，比较了存在和不存在血红素加氧酶时血红素降解的酶促机制。从纯化的 NADPH-细胞色素 P-450 还原酶催化的[14C]高铁白蛋白降解中回收的 14CO 是每摩尔降解的血红素释放 1 分子 CO 的预测值的 15%。 14CO2 和 [14C]甲酸的形成量（分别为 18% 和 98%），表明每个降解的血红素都会氧化裂解多个亚甲基桥，类似于 H2O2 导致的血红素降解。该反应受到过氧化氢酶的强烈抑制，但超氧化物歧化酶没有影响。 [14C]血红素被重构的血红素加氧酶系统降解产生33%的14CO。添加过氧化氢酶以消除副反应后，实现了 14CO 的接近化学计量的回收。使用脾微粒体制剂也实现了 14CO 的接近定量回收。纯化的 NADPH-细胞色素 P-450 还原酶对血红素的降解似乎是由 H2O2 介导的。主要产物不是胆色素，仅形成少量CO。血红素加氧酶的存在，以及可能完整的膜结构，对于血红素有效降解为胆汁色素至关重要，可能是通过保护血红素免受活性氧的不加区别的攻击。
Physiological heme degradation is mediated by the heme oxygenase system consisting of heme oxygenase and NADPH-cytochrome P-450 reductase. Biliverdin IX.alpha. is formed by elimination of one methene bridge C atom as CO. Purified NADPH-cytochrome P-450 reductase alone will also degrade heme but biliverdin is a minor product (15%). The enzymatic mechanisms of heme degradation in the presence and absence of heme oxygenase were compared by analyzing the recovery of 14CO from the degradation of [14C]heme. 14CO recovery from purified NADPH-cytochrome P-450 reductase-catalyzed degradation of [14C]methemalbumin was 15% of the predicted value for 1 molecule of CO liberated/mol of heme degraded. 14CO2 and [14C]formic acid were formed in amounts (18 and 98%, respectively), suggesting oxidative cleavage of more than one methene bridge per heme degraded, similar to heme degradation by H2O2. The reaction was strongly inhibited by catalase, but superoxide dismutase had no effect. [14C]Heme degradation by the reconstituted heme oxygenase system yielded 33% 14CO. Near-stoichiometric recovery of 14CO was achieved after addition of catalase to eliminate side reactions. Near-quantitative recovery of 14CO was also achieved using spleen microsomal preparations. Heme degradation by purified NADPH-cytochrome P-450 reductase appeared to be mediated by H2O2. The major products were not bile pigments, and only small amounts of CO were formed. The presence of heme oxygenase, and possibly an intact membrane structure, were essential for efficient heme degradation to bile pigments, possibly by protecting the heme from indiscriminate attack by active oxygen species.