Modulation of ornithine decarboxylase activity in Escherichia coli by positive and negative effectors.

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Abstract
Two effectors of ornithine decarboxylase (ODC; L-ornithine carboxy-lyase, EC 4.1.1.17) were extracted from an ODC- (speC-) mutant, E. coli MA 255. One of these is an ODC inhibitor (MW 15,000 .+-. 2000) that is labile to trypsin; its activity increases 20-fold in response to increased polyamine levels in the growth medium. It has additional characteristics similar to those of the ODC antizyme of eukaryote cells: it is a noncompetitive inhibitor of ODC; the complex formed between ODC and the ODC inhibitor can be dissociated with salt to provide active ODC and active ODC inhibitor; furthermore, this E. coli ODC inhibitor is inhibitory to eukaryote ODC. A thermostable nondialyzable factor that activates ODC in vitro was also extracted from MA255; increased polyamine levels in the growth medium caused a 1.6-fold increase in the activity of this ODC activator. Effectors with comparable activities were also identified in the parent ODC+ (speC+) strain MA197. The fluctuations of the intracellular levels of these 2 ODC effectors during the growth of E. coli MA255 were related to the temporal changes of the activity of ODC in the parent ODC+ MA197 strain. The mode of interaction of these 3 macromolecules, as reflected in the changes of the activity of ODC, appears to be complex. ODC activity may be controlled post-translationally by macromolecules that act as positive and negative effectors and whose levels fluctuate in reaction.