The threonine-sensitive homoserine dehydrogenase and aspartokinase activities of Escherichia coli

Abstract

1.1. Homoserine dehydrogenase I (L-homoserine: NADP+ oxidoreductase, EC 1.1.1.3) of Escherichia coli is inactivated in two steps by p-mercuribenzoic acid (PMB). The first inactivation step is accompanied by desensitization of the enzyme activity towards its allosteric effector, L-threonine. The desensitized dehydrogenase activity is protected against further action of PMB by its own substrates and by the substrates of the associated activity, aspartokinase I (ATP:L-aspartate 4-phosphotransferase, EC 2.7.2.4).2.2. ATP and aspartate, the substrates of the kinase reaction induce conformational changes in the part of the complex enzyme molecule responsible for the dehydrogenase atalytic activity. 1. Homoserine dehydrogenase I (L-homoserine: NADP+ oxidoreductase, EC 1.1.1.3) of Escherichia coli is inactivated in two steps by p-mercuribenzoic acid (PMB). The first inactivation step is accompanied by desensitization of the enzyme activity towards its allosteric effector, L-threonine. The desensitized dehydrogenase activity is protected against further action of PMB by its own substrates and by the substrates of the associated activity, aspartokinase I (ATP:L-aspartate 4-phosphotransferase, EC 2.7.2.4). 2. ATP and aspartate, the substrates of the kinase reaction induce conformational changes in the part of the complex enzyme molecule responsible for the dehydrogenase atalytic activity.