Um H D, Klein C
Department of Biochemistry and Molecular Biology, St. Louis University School of Medicine, Missouri 63104.
J Protein Chem. 1994 Feb;13(2):177-85. doi: 10.1007/BF01891976.
We have previously shown that micromolar concentrations of GDP stimulate the GTP-mediated phosphorylation of p36, the alpha subunit of succinyl-CoA synthetase (SCS), in lysates prepared from Dictyostelium discoideum. In this study, we report that this phenomenon represents an enhanced catalytic capacity of SCS to form the phosphoenzyme intermediate. Low concentrations of GDP stimulate phosphoenzyme formation by either GTP, or succinyl-CoA and P(i). Under these conditions GDP enhances the apparent rate of phosphoenzyme formation but does not significantly alter the fraction of phosphorylated enzyme. This effect is retained during purification of the protein and is also observed with purified pig heart SCS, indicating that GDP directly alters the enzyme to enhance its rate of phosphorylation. Under these conditions, GDP does not function at the catalytic site, implying an allosteric regulation of SCS.
我们之前已经表明，在从盘基网柄菌制备的裂解物中，微摩尔浓度的GDP会刺激琥珀酰辅酶A合成酶（SCS）的α亚基p36的GTP介导的磷酸化。在本研究中，我们报告这一现象代表了SCS形成磷酸酶中间体的催化能力增强。低浓度的GDP会刺激由GTP、琥珀酰辅酶A和无机磷酸形成磷酸酶。在这些条件下，GDP提高了磷酸酶形成的表观速率，但不会显著改变磷酸化酶的比例。这种效应在蛋白质纯化过程中得以保留，并且在纯化的猪心SCS中也能观察到，这表明GDP直接改变酶以提高其磷酸化速率。在这些条件下，GDP不在催化位点起作用，这意味着SCS存在变构调节。
