Whittaker M M, Barynin V V, Antonyuk S V, Whittaker J W
Department of Biochemistry and Molecular Biology, Oregon Graduate Institute of Science and Technology, Portland 97291-1000, USA.
Biochemistry. 1999 Jul 13;38(28):9126-36. doi: 10.1021/bi990499d.
Manganese catalases contain a binuclear manganese cluster that catalyzes the redox dismutation of hydrogen peroxide, interconverting between dimanganese(II) [(2,2)] and dimanganese(III) [(3,3)] oxidation states during turnover. We have investigated the oxidized (3,3) states of the homologous enzymes from Thermus thermophilus and Lactobacillus plantarum using a combination of optical absorption, CD, MCD, and EPR spectroscopies as sensitive probes of the electronic structure and protein environment for the active site metal clusters. Comparison of results for these two enzymes allows the essential features of the active sites to be recognized and the differences identified. For both enzymes, preparations having the highest catalytic activity have diamagnetic ground states, consistent with the bis-mu-bridging dimanganese core structure that has been defined crystallographically. Oxidative damage and exogenous ligand binding perturb the core structure of LPC, converting the enzyme to a distinct form in which the cluster becomes paramagnetic as a result of altered exchange coupling mediated by the bridging ligands. The TTC cluster does not exhibit this sensitivity to ligand binding, implying a different reactivity for the bridges in that enzyme. A mechanism is proposed involving distinct coordination modes for peroxide substrate in each of the two half-reactions for enzyme turnover.
锰过氧化氢酶含有一个双核锰簇，该簇催化过氧化氢的氧化还原歧化反应，在反应过程中，二价锰（[(2,2)]）和三价锰（[(3,3)]）氧化态之间相互转换。我们结合使用光吸收、圆二色光谱（CD）、磁圆二色光谱（MCD）和电子顺磁共振光谱（EPR），作为活性位点金属簇电子结构和蛋白质环境的灵敏探针，研究了嗜热栖热菌和植物乳杆菌同源酶的氧化态（3,3）。比较这两种酶的结果，有助于识别活性位点的基本特征并找出差异。对于这两种酶，具有最高催化活性的制剂具有抗磁性基态，这与晶体学确定的双μ-桥连双核锰核心结构一致。氧化损伤和外源性配体结合会扰乱植物乳杆菌过氧化氢酶（LPC）的核心结构，使该酶转变为一种独特的形式，由于桥连配体介导的交换耦合改变，簇变得顺磁性。嗜热栖热菌过氧化氢酶（TTC）簇对配体结合不表现出这种敏感性，这意味着该酶中桥的反应性不同。我们提出了一种机制，该机制涉及酶反应过程中两个半反应中每个反应的过氧化物底物的不同配位模式。
