The role of isocitrate in control of the phosphorylation of isocitrate dehydrogenase in Escherichia coli ML308

Isocitrate dehydrogenase from Escherichia coli is regulated by a reversible phosphorylation mechanism. We confirm here that this permits intracellular isocitrate to rise to a level that can sustain growth on acetate. Isocitrate inhibits isocitrate dehydrogenase kinase and activates isocitrate dehydrogenase phosphatase in vitro. Addition of pyruvate to cultures growing on acetate causes reversible dephosphorylation and activation of isocitrate dehydrogenase, and we show here that this is accompanied by a transient two‐fold increase in the intracellular concentration of isocitrate. The data support our suggestion that isocitrate can play a key role in controlling the phosphorylation state of isocitrate dehydrogenase in vivo