Dalton H, Lowe D J, Pawlik T, Bray R C
Biochem J. 1976 Feb 1;153(2):287-95. doi: 10.1042/bj1530287.
E.p.r- (electron-paramagnetic-resonance) spectroscopy was used to compare chemical environment and reactivity of molybdenum, flavin and iron-sulphur centres in the enzyme xanthine dehydrogenase from Veillonella alcalescens (Micrococcus lactilyticus) with those of the corresponding centres in milk xanthine oxidase. The dehydrogenase is frequently contaminated with small but variable amounts of a species resistant to oxidation and giving a new molybdenum (V) e.p.r. signal, "Resting I". There is also a "desulpho" form of the enzyme giving a Slow Mo(V) signal, indistinguishable from that of the milk enzyme. Molybdenum of the active enzyme behaves in a manner analogous to that of the milk enzyme, giving a Rapid Mo(V) signal on partial reduction with substrates or dithionite. Detailed comparison shows that molybdenum in each enzyme must have the same ligand atoms arranged in the same manner. As with the milk enzyme, complex-formation between reduced dehydrogenase and purine substrate molecules, presumably interacting at the normal substrate-binding site, modifies the Rapid signal, confirming that such substrates interact near molybdenum. The dehydrogenase-flavin semiquinone signal is identical with that of the oxidase but, in contrast, there is only one iron-sulphur signal. The latter gives an e.p.r. spectrum similar to that of aldehyde oxidase.
采用电子顺磁共振（E.p.r）光谱法，比较了产碱韦荣球菌（乳酸微球菌）中的黄嘌呤脱氢酶与乳黄嘌呤氧化酶中相应中心的钼、黄素和铁硫中心的化学环境及反应活性。脱氢酶常被少量但可变的抗氧化物污染，产生一种新的钼（V）电子顺磁共振信号，即“静息I”。此外，该酶还有一种“脱硫”形式，产生的慢钼（V）信号与乳酶的信号无法区分。活性酶中的钼表现与乳酶类似，在被底物或连二亚硫酸盐部分还原时产生快速钼（V）信号。详细比较表明，每种酶中的钼必定具有以相同方式排列的相同配体原子。与乳酶一样，还原型脱氢酶与嘌呤底物分子之间的复合物形成（推测在正常底物结合位点相互作用）会改变快速信号，证实此类底物在钼附近相互作用。脱氢酶 - 黄素半醌信号与氧化酶的相同，但与之相反，只有一个铁硫信号。后者产生的电子顺磁共振光谱与醛氧化酶的类似。
