The methionine-repressible homoserine dehydrogenase and aspartokinase activities of Escherichia coli K 12. Preparation of the homogeneous protein catalyzing the two activities. Molecular weight of the native enzyme and of its subunits.

Abstract

The complex protein carrying the two methionine-repressible activities aspartokinase II and homoserine dehydrogenase II has been obtained in a homogeneous state from extracts of a genetically derepressed mutant of Escherichia coli K 12. Some general properties are described. The enzyme has a molecular weight of 169,000. In the presence of 6 M guanidine and 0.1 M mercaptoethanol, it undergoes dissociation into subunits which have a molecular weight of 43,000. The enzyme appears thus composed of four subunits of identical size.