Pienkos P T, Shah V K, Brill W J
Proc Natl Acad Sci U S A. 1977 Dec;74(12):5468-71. doi: 10.1073/pnas.74.12.5468.
A molybdenum cofactor (Mo-co) from xanthine oxidase (xanthine:oxygen oxidoreductase, EC 1.2.3.2) can be isolated from the enzyme by a technique that has been used to isolate an iron-molybdenum cofactor (FeMo-co) from component I of nitrogenase. N-Methylformamide is used for the extraction of these molybdenum cofactors. Mo-co from xanthine oxidase activates nitrate reductase (NADPH:nitrate oxidoreductase, EC 1.6.6.2) in an extract from Neurospora crassa mutant strain Nit-1; however, FeMo-co is unable to activate nitrate reductase in strain Nit-1. Mo-co from xanthine oxidase is unable to activate nitrogenase in an extract of Azotobacter vinelandii mutant strain UW45. Inactive component I in this extract can be activated by FeMo-co. These results indicate that nitrate reductase and xanthine oxidase share a common molybdenum cofactor, but this cofactor is different from the molybdenum cofactor in nitrogenase.A. vinelandii synthesizes both Mo-co and FeMo-co. Mo-co is produced when the cells fix N(2) and also when they are repressed for nitrogenase synthesis by growth in a medium containing excess ammonium. However, FeMo-co is not produced when cells are grown in an ammonium-containing medium. Partially purified preparations of component I from A. vinelandii and Klebsiella pneumoniae contain both FeMo-co and Mo-co. The presence of both FeMo-co and Mo-co activities in partially purified preparations of component I explains previous reports of activation of inactive nitrate reductase in strain Nit-1 by acid-treated component I of nitrogenase. The Mo-co can be separated from FeMo-co in these preparations by chromatography on Sephadex G-100 in N-methylformamide. Both FeMo-co and Mo-co are sensitive to oxygen.
可通过一种曾用于从固氮酶组分I中分离铁钼辅因子（FeMo-co）的技术，从黄嘌呤氧化酶（黄嘌呤：氧氧化还原酶，EC 1.2.3.2）中分离出钼辅因子（Mo-co）。N-甲基甲酰胺用于提取这些钼辅因子。来自黄嘌呤氧化酶的Mo-co可激活粗糙脉孢菌突变株Nit-1提取物中的硝酸还原酶（NADPH：硝酸氧化还原酶，EC 1.6.6.2）；然而，FeMo-co无法激活Nit-1菌株中的硝酸还原酶。来自黄嘌呤氧化酶的Mo-co无法激活维涅兰德固氮菌突变株UW45提取物中的固氮酶。该提取物中无活性的组分I可被FeMo-co激活。这些结果表明，硝酸还原酶和黄嘌呤氧化酶共享一种共同的钼辅因子，但该辅因子与固氮酶中的钼辅因子不同。维涅兰德固氮菌可合成Mo-co和FeMo-co。当细胞固定N₂时以及当它们在含有过量铵的培养基中生长而被抑制固氮酶合成时，都会产生Mo-co。然而，当细胞在含铵培养基中生长时，不会产生FeMo-co。来自维涅兰德固氮菌和肺炎克雷伯菌的组分I的部分纯化制剂中同时含有FeMo-co和Mo-co。组分I的部分纯化制剂中同时存在FeMo-co和Mo-co活性，这解释了先前关于固氮酶的酸处理组分I激活Nit-1菌株中无活性硝酸还原酶的报道。在这些制剂中，可通过在N-甲基甲酰胺中用葡聚糖凝胶G-100进行色谱分离，将Mo-co与FeMo-co分开。FeMo-co和Mo-co都对氧气敏感。
