McKee J S, Nimmo H G
Department of Biochemistry, University of Glasgow, Scotland, U.K.
Biochem J. 1989 Jul 1;261(1):301-4. doi: 10.1042/bj2610301.
The arginine-specific reagent phenylglyoxal inactivated the active, dephosphorylated, form of Escherichia coli isocitrate dehydrogenase rapidly in a pseudo-first-order process. Both NADP+ and NADPH protected the enzyme against inactivation. Phenylglyoxal appeared to react with one arginine residue per subunit, and the extent of the reaction was proportional to the extent of the inactivation. In contrast, the phosphorylated form of isocitrate dehydrogenase did not react detectably with phenylglyoxal. The data indicate that the coenzyme-binding site of isocitrate dehydrogenase contains a reactive arginine residue that is protected by phosphorylation, and are consistent with the hypothesis that phosphorylation of the enzyme occurs close to or at its active site.
精氨酸特异性试剂苯乙二醛能使活性的、去磷酸化形式的大肠杆菌异柠檬酸脱氢酶在准一级反应过程中迅速失活。NADP⁺和NADPH都能保护该酶不被失活。苯乙二醛似乎与每个亚基的一个精氨酸残基发生反应，且反应程度与失活程度成正比。相比之下，磷酸化形式的异柠檬酸脱氢酶与苯乙二醛没有可检测到的反应。这些数据表明，异柠檬酸脱氢酶的辅酶结合位点含有一个可被磷酸化保护的活性精氨酸残基，这与该酶的磷酸化发生在其活性位点附近或活性位点处的假设一致。
