Crans D C, Simone C M
Department of Chemistry, Colorado State University, Fort Collins 80523.
Biochemistry. 1991 Jul 9;30(27):6734-41. doi: 10.1021/bi00241a015.
The inhibitory effects of vanadium(V) were determined on the oxidation of glycerol 3-phosphate (G3P) catalyzed by glycerol-3-phosphate dehydrogenase (G3PDH), an enzyme with a thiol group in the active site. G3PDH from rabbit muscle was inhibited by vanadate, and the active inhibiting species were found to be the vanadate dimer and/or tetramer. The dimer was a sufficiently weak inhibitor at pH 7.4 with respect to G3P; the tetramer could account for all the observed inhibition. The tetramer was a competitive inhibitor with respect to G3P with a Ki of 0.12 mM. Both the dimer and tetramer were noncompetitive inhibitors at pH 7.4 with respect to NAD with Ki's of 0.36 mM and 0.67 mM. G3PDH inhibited by vanadate was reactivated when EDTA complexed the vanadate. The reactivation occurred even after extended periods of incubation of G3PDH and vanadate, suggesting that the inhibition is reversible despite the thiol group in the active site. Analogous reactivation is also observed with glyceraldehyde-3-phosphate dehydrogenase (Gly3PDH). Gly3PDH is an enzyme that previously had been reported to undergo redox chemistry with vanadate. The work described in this paper suggests vanadate will not necessarily undergo redox chemistry with enzymes containing thiol groups exposed on the surface of the protein.
测定了钒（V）对甘油-3-磷酸脱氢酶（G3PDH，一种活性位点含有硫醇基团的酶）催化的甘油3-磷酸（G3P）氧化的抑制作用。来自兔肌肉的G3PDH受到钒酸盐的抑制，发现活性抑制物质是钒酸盐二聚体和/或四聚体。在pH 7.4时，二聚体对G3P的抑制作用较弱；四聚体可以解释所有观察到的抑制作用。四聚体是G3P的竞争性抑制剂，Ki为0.12 mM。在pH 7.4时，二聚体和四聚体都是NAD的非竞争性抑制剂，Ki分别为0.36 mM和0.67 mM。当EDTA与钒酸盐络合时，被钒酸盐抑制的G3PDH会重新激活。即使在G3PDH和钒酸盐长时间孵育后仍会发生重新激活，这表明尽管活性位点存在硫醇基团，抑制作用仍是可逆的。在甘油醛-3-磷酸脱氢酶（Gly3PDH）中也观察到类似的重新激活。Gly3PDH是一种先前已报道会与钒酸盐发生氧化还原反应的酶。本文所述的工作表明，钒酸盐不一定会与蛋白质表面暴露有硫醇基团的酶发生氧化还原反应。
