Goubeaud M, Schreiner G, Thauer R K
Max-Planck-Institut für terrestrische Mikrobiologie, Philipps-Universität, Marburg, Germany.
Eur J Biochem. 1997 Jan 15;243(1-2):110-4. doi: 10.1111/j.1432-1033.1997.00110.x.
The nickel porphinoid, coenzyme F430, is the prosthetic group of methyl-coenzyme M reductase. The active form of the enzyme exhibits Ni-EPR signals designated as MCR-red1 and MCR-red2. The inactive form of the enzyme is either EPR silent or it exhibits a distinct Ni-EPR signal designated MCR-ox1. Evidence is presented here that the MCR-ox1 form of the enzyme can be converted in vitro to the MCR-red1 form by reduction with titanium(III) citrate at pH 9. During conversion, the specific activity increases with increasing MCR-red1 spin concentration from 2 U/mg to approximately 100 U/mg at spin concentrations higher than 80%. The reduced methyl-coenzyme-M reductase shows an ultraviolet/visible spectrum characteristic for coenzyme F430 in the Ni(I) oxidation state, with maxima at 386 nm and at 750 nm. The results indicate that methyl-coenzyme-M reductase is activated when the enzyme-bound coenzyme F430 is reduced to the Ni(I) oxidation state. The experiments were performed with purified methyl-coenzyme-M reductase isoenzyme I of Methanobacterium thermoautotrophicum (strain Marburg).
镍卟啉类辅酶F430是甲基辅酶M还原酶的辅基。该酶的活性形式呈现出被指定为MCR-red1和MCR-red2的镍电子顺磁共振（EPR）信号。该酶的无活性形式要么是EPR沉默的，要么呈现出一个被指定为MCR-ox1的独特镍EPR信号。本文提供的证据表明，该酶的MCR-ox1形式在体外通过在pH 9下用柠檬酸钛还原可转化为MCR-red1形式。在转化过程中，比活性随着MCR-red1自旋浓度的增加而增加，在自旋浓度高于80%时从2 U/mg增加到约100 U/mg。还原后的甲基辅酶M还原酶显示出Ni(I)氧化态下辅酶F430的紫外/可见光谱特征，在386 nm和750 nm处有最大值。结果表明，当与酶结合的辅酶F430被还原到Ni(I)氧化态时，甲基辅酶M还原酶被激活。实验是用嗜热自养甲烷杆菌（马尔堡菌株）纯化的甲基辅酶M还原酶同工酶I进行的。
