Characterization of a meso-diaminopimelate-sensitive aspartate kinase from cyanobacteria

A diaminopimelate-sensitive aspartate kinase isozyme was identified in extracts of the cyanobacteria Anabaena PCC7120 and Synechococcus PCC7002 and purified 2800-fold to homogeneity. The Mr of the enzyme was 110 000 and 55 000, respectively, under non-denaturing and denaturing conditions, suggesting that the cyanobacterial diaminopimelate-sensitive aspartokinase is a dimer composed of identical subunits. meso-Diaminopimelate produced half-maximal inhibition at 0.4 mM. Inhibition by 5 mM meso-diaminopimelate varied between 50 and 80% with different enzyme preparations, probably owing to partial desensitization to allosteric inhibition. The diaminopimelate-sensitive aspartate kinase described here is the first such isozyme reported outside the sporulating Gram-positive genera Bacillus and Clostridium, and its possible function in cyanobacteria is discussed.