Nemani R, Lee E Y
Department of Veterans Affairs Medical Center, St. Louis, Missouri 63125.
Arch Biochem Biophys. 1993 Jan;300(1):24-9. doi: 10.1006/abbi.1993.1004.
Chemical modification of the sulfhydryl residues of the catalytic subunits of protein phosphatases 1 and 2A was studied. Both enzymes were inactivated by a variety of thiol group reagents. Mercurial compounds were the most effective inactivators. Of the alkylating agents the maleimides were more effective than iodoacetate or iodoacetamide which were relatively slow reacting. Both enzymes were also inactivated by disulfides, including glutathione disulfide, 5,5'-dithiobis(2-nitrobenzoic acid), and 4,4'-dipyridyl disulfide. The latter two were much more reactive than glutathione disulfide and, in addition, displayed a significant differential reactivity toward phosphatase 1. The apparent second-order rate constants for the inactivation of phosphatase 1 were 20- to 70-fold higher than for phosphatase 2A with 5,5'-dithiobis(2-nitrobenzoic acid) and 4,4'-dipyridyl disulfide. Kinetic analysis indicated that inactivation of both enzymes could be correlated with the modification of one cysteine per one mole of enzyme.
对蛋白磷酸酶1和2A催化亚基的巯基残基进行了化学修饰研究。这两种酶都被多种巯基试剂灭活。汞化合物是最有效的灭活剂。在烷基化试剂中，马来酰亚胺比反应相对较慢的碘乙酸或碘乙酰胺更有效。这两种酶也被二硫化物灭活，包括谷胱甘肽二硫化物、5,5'-二硫代双(2-硝基苯甲酸)和4,4'-二吡啶二硫化物。后两者比谷胱甘肽二硫化物反应性更强，此外，对磷酸酶1表现出显著的差异反应性。用5,5'-二硫代双(2-硝基苯甲酸)和4,4'-二吡啶二硫化物使磷酸酶1失活的表观二级速率常数比磷酸酶2A高20至70倍。动力学分析表明，两种酶的失活都与每摩尔酶中一个半胱氨酸的修饰有关。
