J Integr Plant Biol. ›› 1981, Vol. 23 ›› Issue (1): -.

• Research Articles •    

The Active Components of Methyl Viologen-Nitrate Reductase in Xanthine Oxidase

Shen Jian-xia, Wang Zong-ce, Xin Shu-ying and Yen Long-fei   

Abstract: The components of the active molybdenum cofactor in xanthine oxidase was found. The molybdenum cofactor is responsible for the enzymatic activity of the methyl viologen-nitrate reduction. The inactivation of the methyl viologen-nitrate reductase by cyanide is accompanied by the extraction of sulfur from the enzyme. Cyanide inactivated enzyme can be reactivated by incubation with Na2S. The results suggest that the active site of the methyl viologen-nitrate reductase contains an atom of active sulfur which does not originate from the acid labile sulfur of the Fe/S cluster, neither originate from the organic sulfur of the cysteine residue, nor from the sulfur of persulfide. It is probably another type of inorganic sulfur near the molybdenum atoms, The flavin-free xanthine oxidase may be loss entirely its oxidation activity of xanthine to uric acid. In contrast, the activity of the methyl viologen-nitrate reductase is nearly completly insensitive to the flavinfree treatment. Studies on the Fe-free xanthine oxidase, obtained by metal-binding agent phenanthroline and by acid treatment, revealed Fe (in xanthine oxidase it is the Fe of the Fe/S cluster) is also one of the active conponents, functioning in the methyl viologen-nitrate reductase, besides molybdenum.

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