The threonine-sensitive homoserine dehydrogenase and aspartokinase activities of Escherichia coli K-12. Incubation of the enzyme in alkaline conditions: dissociation and disulfide-bridge formation.
Aspartokinase I - homoserine dehydrogenase I from Escherichia coli K-12, a homotetrameric enzyme, dissociates into dimers upon alkaline treatment. Both aspartokinase and homoserine dehydrogenase inactivation, as well as desensitazion towards L-threonine, occur in a multi-step process. Dithiothreitol stabilizes a dimeric form retaining full activity and sensitivity; L-homoserine stabilizing another dimeric form devoid of aspartokinase activity and retaining a substantial dehydrogenase activity insensitive toward L-threonine. A model is proposed showing that dissociation into dimers occurs in a first step, the resulting dimer losing both aspartokinase and homoserine dehydrogenase sensitivity in two subsequent steps involving the formation of intrachain disulfide bonds.
D000429:Alcohol Oxidoreductases / Q000378:metabolism*; D001222:Aspartate Kinase / Q000378:metabolism*; D001665:Binding Sites; D004220:Disulfides / Q000032:analysis; D004228:Dithionitrobenzoic Acid / Q000494:pharmacology; D004229:Dithiothreitol / Q000494:pharmacology; D004926:Escherichia coli / Q000201:enzymology*; D006714:Homoserine / Q000494:pharmacology; D006715:Homoserine Dehydrogenase / Q000378:metabolism*; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D046911:Macromolecular Substances; D008970:Molecular Weight; D009097:Multienzyme Complexes / Q000378:metabolism; D010770:Phosphotransferases / Q000378:metabolism*; D011485:Protein Binding; D011487:Protein Conformation; D013912:Threonine / Q000494:pharmacology
D004220:Disulfides; D046911:Macromolecular Substances; D009097:Multienzyme Complexes; D013912:Threonine; D006714:Homoserine; D004228:Dithionitrobenzoic Acid; D000429:Alcohol Oxidoreductases; D006715:Homoserine Dehydrogenase; D010770:Phosphotransferases; D001222:Aspartate Kinase; D004229:Dithiothreitol