Aspartokinase of Myxococcus xanthus: "feedback stimulation" by required amino acids

The aspartokinase activity found in extracts of the bacterium Myxococcus xanthus was subject to feedback inhibition and feedback repression by l-threonine and l-lysine. Both types of inhibition were essentially additive. The required amino acids, l-isoleucine and l-methionine, caused considerable increase in the activity of the enzyme. This phenomenon is referred to as "feedback stimulation." The polyamine, spermidine, exerted strong enhancement of the activity even at 0.1 mM. Meso-diaminopimelate, although not inhibitory by itself, abolished the activation exerted by either l-isoleucine or l-methionine. The possible physiological significance of interactions between the various effectors is discussed.