Spin-spin interaction between molybdenum and one of the iron-sulphur systems of xanthine oxidase and its relevance to the enzymic mechanism.
Spin-spin interaction between molybdenum and one of the iron-sulphur systems of xanthine oxidase and its relevance to the enzymic mechanism.
复制标题
钼与黄嘌呤氧化酶的铁-硫系统之一之间的自旋相互作用及其与酶机制的相关性。
DOI：
10.1042/bj1300239
复制
发表时间：
1972
影响因子：
4.1
通讯作者：
R. Bray
中科院分区：
文献类型：
--
作者：
D. Lowe;Ruth M. Lynden;R. Bray
1.电子顺磁共振在氦温度下在9和35 GHz的研究已经给出了关于黄嘌呤氧化酶的结构和作用机制的新信息。2.正如其他人所报道的，这种酶产生两种类型的e.p.r.。信号归因于铁硫系统。第一个是g（av.）= 1.95.第二个参数为g（1）2.12，g（2）2.007和g（3）1.91，其中g（平均）= 2.01.该物种似乎具有比前一种稍高的氧化还原电位。3. Mo（v）e.p.r.在某些条件下观察到的来自酶的信号表明是由于Mo（v）和g（av.）之间的弱自旋-自旋相互作用。1.95 Fe/S。对于慢Mo（v）信号，已经对该现象进行了最充分的研究。这里，光谱变化采取附加的近似各向同性的11 G分裂的形式，仅在约45 K以下检测到。未还原Fe/S的样品光谱无明显变化。4.在快速冷冻实验中获得的快速Mo（V）信号中观察到类似的光谱变化，但仅在与底物反应时间相对较长的样品中观察到。因此，这一现象可能提供了一种区分仅还原Mo的酶中心与Mo和Fe/S均还原的酶中心的方法。5.额外的快速冷冻数据倾向于支持一个两个，而不是一个电子转移的还原当量从基板黄嘌呤氧化酶的报告。
1. Electron-paramagnetic-resonance (e.p.r.) studies at 9 and 35GHz at helium temperatures have given new information relating to the structure and mechanism of action of xanthine oxidase. 2. As reported by others, the enzyme gives two types of e.p.r. signal attributed to iron-sulphur systems. The first has g(av.)=1.95. Parameters of the second are determined as g(1) 2.12, g(2) 2.007 and g(3) 1.91, with g(av.)=2.01. This species seems to have a slightly higher redox potential than the former one. 3. Temperature-dependent changes in the form of Mo(v) e.p.r. signals from the enzyme, observed under certain conditions, are shown to be due to weak spin-spin interaction between Mo(v) and g(av.)=1.95 Fe/S. The phenomenon has been studied most fully for the Slow Mo(v) signal. Here, the spectral change takes the form of an additional approximately isotropic 11G splitting, detected below about 45 degrees K only. Samples without Fe/S reduced showed no such changes of spectrum. 4. Similar spectral changes were observed in the Rapid Mo(v) signals, obtained in rapid-freezing experiments, but only in samples corresponding to relatively long reaction times with the substrate. It is suggested therefore that the phenomenon may provide a means of distinguishing enzyme centres with Mo only reduced from those in which both Mo and Fe/S are reduced. 5. Additional rapid-freezing data tending to support a two- rather than a one-electron transfer of reducing equivalents from substrates to xanthine oxidase are reported.