The NIFS protein can function as a selenide delivery protein in the biosynthesis of selenophosphate

被引:60
作者
Lacourciere, GM [1 ]
Stadtman, TC [1 ]
机构
[1] NHLBI, Biochem Lab, NIH, Bethesda, MD 20892 USA
关键词
D O I
10.1074/jbc.273.47.30921
中图分类号
Q5 [生物化学]; Q7 [分子生物学];
学科分类号
071010 ; 081704 ;
摘要
The NIFS protein from Azobacter vinelandii is a pyridoxal phosphate-containing homodimer that catalyzes the formation of equimolar amounts of elemental sulfur and L-alanine from the substrate L-cysteine (Zheng, L,, White, R, H,, Cash, V, L,, Jack, R, F,, and Dean, D. R, (1993) Proc. Natl, Acad Sci, U.S.A. 90, 2754-2758), A sulfur transfer role of NIFS in which the enzyme donates sulfur for iron sulfur center formation in nitrogenase was suggested. The fact that NIFS also can catalyze the decomposition of L-selenocysteine to elemental selenium and L-alanine suggested the possibility that this enzyme might serve as a selenide delivery protein for the in vitro biosynthesis of selenophosphate. In agreement with this hypothesis, we have shown that replacement of selenide with NIFS and L-selenocysteine in the in vitro selenophosphate synthetase assay results in an increased rate of formation of selenophosphate. These results thus support the view that a selenocysteine specific enzyme similar to NIFS may be involved as an in vivo selenide delivery protein for selenophosphate biosynthesis. A kinetic characterization of the two NIFS catalyzed reactions carried out in the present study indicates that the enzyme favors L-cysteine as a substrate compared with its selenium analog. A specific activity for L-cysteine of 142 nmol/min/mg compared with 55 nmol/min/mg for L-selenocysteine was determined. This level of enzyme activity on the selenoamino acid substrate is adequate to deliver selenium to selenophosphate synthetase in the in vitro assay system described.
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页码:30921 / 30926
页数:6
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