Phosphorylation of isocitrate dehydrogenase in Escherichia coli mutants with a non-functional glyoxylate cycle

The phosphorylation of NADP-specific isocitrate dehydrogenase in an isocitrate lyase and in a malate synthase mutant of Escherichia coli has been investigated. The results clearly demonstrate that isocitrate dehydrogenase may undergo an acetate-induced phosphorylation in organisms which do not have a functional glyoxylate cycle. This observation, together with those reported in Salmonella typhimurium, suggest that the current notion concerning the interrelationship between the glyoxylate cycle and the reversible phosphorylation of NADP-isocitrate dehydrogenase in microbial physiology should be reevaluated, and that phosphoenolpyruvate may be a key factor in the regulation of the reversible covalent modification of this enzyme in vivo.