Heterotetrameric sarcosine oxidase (TSOX) is a complex bifunctional flavoenzyme that contains two flavins. Most of the FMN in recombinant TSOX is present as a covalent adduct with an endogenous ligand. Enzyme denaturation disrupts the adduct, accompanied by release of a stoichiometric amount of sulfide. Enzyme containing>or=90% unmodified FMN is prepared by displacement of the endogenous ligand with sulfite, a less tightly bound competing ligand. Reaction of adduct-depleted TSOX with sodium sulfide produces a stable complex that resembles the endogenous TSOX adduct and known 4a-S-cysteinyl flavin adducts. The results provide definitive evidence for sulfide as the endogenous TSOX ligand and strongly suggest that the modified FMN is a 4a-sulfide adduct. A comparable reaction with sodium sulfide is not detected with other flavoprotein oxidases. A model of the postulated TSOX adduct suggests that it is stabilized by nearby residues that may be important in the electron transferase/oxidase function of the coenzyme.

译文

:异四聚体肌氨酸氧化酶(TSOX)是一种复杂的双功能黄素酶,其中含有两个黄素。重组TSOX中的大多数FMN以与内源性配体的共价加合物形式存在。酶变性会破坏加合物,并释放出化学计量的硫化物。通过用亚硫酸盐(一种不太紧密结合的竞争性配体)置换内源配体来制备含≥90%或未修饰的FMN的酶。耗尽加合物的TSOX与硫化钠的反应产生了一种稳定的络合物,类似于内源性TSOX加合物和已知的4a-S-半胱氨酰黄素加合物。结果为硫化物作为内源性TSOX配体提供了确凿的证据,并强烈表明修饰的FMN是4a-硫化物加合物。其他黄素蛋白氧化酶未检测到与硫化钠可比的反应。假定的TSOX加合物的模型表明它被附近的残基稳定了,这些残基可能对辅酶的电子转移酶/氧化酶功能很重要。

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