Molybdenum selenites

Sasaki et al. [880ZE/YAG] studied the - MoOj -SeOP system at 298.15 K by po-tentiometric and Se NMR measurements in 1 M NaCl. The equilibrium analysis based on the general reaction scheme  

The formation of the heteropolyanions SejMOjO established and accepted, whereas the formation of the (14,8,2) and (15,8,2) species is tentative, see Appendix A. No attempt to extrapolate the data to standard conditions has been made. 

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Stadtman 1971 Kung et al. 1971). Degradation is initiated by hydroxylation of the ring, and the level of nicotinic acid hydroxylase is snbstantially increased by the addition of selenite to the medinm (Imhoff and Andreesen 1979). Nicotinate hydroxylase from Clostridium barkeri contains molybdenum that is coordinated to seleninm, which is essential for hydroxylase activity (Gladyshev et al. 1994). The most remarkable featnre of the pathway is the mechanism whereby 2-methylene-glntarate is converted into methylitaconate by a coenzyme Bi2-mediated reaction (Knng and Stadtman 1971). 

Another selenium-containing molybdenum hydroxylase that has been isolated from Clostridium barkeri (identical to Eubacterium barkeri) is nicotinic acid hydroxylase (NAH). Clostridium barkeri was isolated initially as a fermentor of nicotinic acid and thus NAH is a key enzyme in the efficient fermentation of nicotinic acid as a source of carbon and energy. NAH contained selenium when purified from cells labeled with Se-selenite. However, this label was lost during denaturing gel electrophoresis and also on heating of the enzyme (Dilworth 1982). Exhaustive analysis of selenium-labeled alkylation products of NAH under various conditions revealed selenium was bound as a labile cofactor (Dilworth 1982), and not as seleno-cysteine. This report was the first to describe a selenium-dependent enzyme that did not contain selenium in the form of selenocysteine. 

Carbon monoxide serves as the sole carbon and energy source for the carboxydo bacteria under aerobic conditions. Using water as the oxygen donor, carbon monoxide oxidase catalyzes the hydroxylation of carbon monoxide, giving carbon dioxide or bicarbonate for assimilation. Most work has been carried out on the enzyme from Pseudomonas carboxydovorans.,ftJ7>W38 The activity of carbon monoxide oxidase is considerably stimulated upon anaerobic treatment with sulfide and dithionite, or by aerobic treatment with selenite. The binding of selenite to the oxidase specifically activates the CO — methylene blue reaction.1039 The molybdenum cofactor liberated from selenium-activated carbon monoxide oxidase does not contain selenium. Here, then, the... 

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