Abstract
Abstract Aspartokinase has been purified approximately 1,300-fold from crude extracts of Bacillus polymyxa. Electrophoresis in polyacrylamide gels and equilibrium ultracentrifugation indicated that the purified enzyme was essentially homogeneous. Aged preparations of the enzyme exhibit two electrophoretic components which can be interconverted by treatment with the feedback inhibitors l-threonine and l-lysine or with MgCl2. The molecular weight and partial specific volume were determined by equilibrium ultracentrifugation to be 116,000 and 0.751 ml per g, respectively. The amino acid composition of the enzyme was analyzed. Upon electrophoresis in polyacrylamide gels in the presence of sodium dodecyl sulfate or urea or after treatment with maleic anhydride, aspartokinase could be resolved into two components of molecular weights about 17,000 and 47,000, respectively. The two types of subunits could be separated be gel filtration on Sephadex G-200 in the presence of sodium dodecyl sulfate. It is concluded that aspartokinase is an oligomeric protein composed of at least two different types of polypeptide chains.
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