人血红素加氧酶-1催化血红素氧化的反应中间体及单周转速率常数

Reaction intermediates and single turnover rate constants for the oxidation of heme by human heme oxygenase-1.

作者信息

Liu Y, Ortiz de Montellano P R

机构信息

Department of Pharmaceutical Chemistry, School of Pharmacy, University of California, San Francisco, California 94143-0446, USA.

出版信息

J Biol Chem. 2000 Feb 25;275(8):5297-307. doi: 10.1074/jbc.275.8.5297.

DOI:10.1074/jbc.275.8.5297

PMID:10681502

Abstract

Heme oxygenase converts heme to biliverdin, iron, and CO in a reaction with two established intermediates, alpha-meso-hydroxyheme and verdoheme. Transient kinetic studies show that the conversion of Fe(3+)-heme to Fe(3+)-verdoheme is biphasic. Electron transfer to the heme (0.11 s(-1) at 4 degrees C and 0.49 s(-1) at 25 degrees C) followed by rapid O(2) binding yields the ferrous dioxy complex. Transfer of an electron (0.056 s(-1) at 4 degrees C and 0.21 s(-1) at 25 degrees C) to this complex triggers the formation of alpha-meso-hydroxyheme and its subsequent O(2)-dependent fragmentation to Fe(3+)-verdoheme. The conversion of Fe(3+)-verdoheme to Fe(3+)-biliverdin is also biphasic. Thus, reduction of Fe(3+) to Fe(2+)-verdoheme (0.15 s(-1) at 4 degrees C and 0.55 s(-1) at 25 degrees C) followed by O(2) binding and an electron transfer produces Fe(3+)-biliverdin (0.025 s(-1) at 4 degrees C and 0.10 s(-1) at 25 degrees C). The conversion of Fe(3+)-biliverdin to free biliverdin is triphasic. Reduction of Fe(3+)-biliverdin (0.035 s(-1) at 4 degrees C and 0.15 s(-1) at 25 degrees C), followed by rapid release of Fe(2+) (0.19 s(-1) at 4 degrees C and 0.39 s(-1) at 25 degrees C), yields the biliverdin-enzyme complex from which biliverdin slowly dissociates (0.007 s(-1) at 4 degrees C and 0.03 s(-1) at 25 degrees C). The rate of Fe(2+) release agrees with the rate of Fe(3+)-biliverdin reduction. Fe(2+) release clearly precedes biliverdin dissociation. In the absence of biliverdin reductase, biliverdin release is the rate-limiting step, but in its presence biliverdin release is accelerated and the overall rate of heme degradation is limited by the conversion of Fe(2+)-verdoheme to the Fe(3+)-biliverdin.

摘要

血红素加氧酶在与两种已确定的中间体α-中羟基血红素和胆绿血红素的反应中，将血红素转化为胆绿素、铁和一氧化碳。瞬态动力学研究表明，Fe(3+) - 血红素向Fe(3+) - 胆绿血红素的转化是双相的。电子转移至血红素（4℃时为0.11 s(-1)，25℃时为0.49 s(-1)），随后快速结合氧气生成亚铁双氧络合物。向该络合物转移一个电子（4℃时为0.056 s(-1)，25℃时为0.21 s(-1)）触发α-中羟基血红素的形成及其随后依赖氧气的裂解为Fe(3+) - 胆绿血红素。Fe(3+) - 胆绿血红素向Fe(3+) - 胆绿素的转化也是双相的。因此，Fe(3+)还原为Fe(2+) - 胆绿血红素（4℃时为0.15 s(-1)，25℃时为0.55 s(-1)），随后结合氧气并进行电子转移产生Fe(3+) - 胆绿素（4℃时为0.025 s(-1)，25℃时为0.10 s(-1)）。Fe(3+) - 胆绿素向游离胆绿素的转化是三相的。Fe(3+) - 胆绿素的还原（4℃时为0.035 s(-1)，25℃时为0.15 s(-1)），随后快速释放Fe(2+)（4℃时为0.19 s(-1)，25℃时为0.39 s(-1)），产生胆绿素 - 酶复合物，胆绿素从该复合物中缓慢解离（4℃时为0.007 s(-1)，25℃时为0.03 s(-1)）。Fe(2+)的释放速率与Fe(3+) - 胆绿素的还原速率一致。Fe(2+)的释放明显先于胆绿素的解离。在没有胆绿素还原酶的情况下，胆绿素的释放是限速步骤，但在其存在时胆绿素的释放加速，血红素降解的总体速率受Fe(2+) - 胆绿血红素向Fe(3+) - 胆绿素转化的限制。