Reversible inactivation of isocitrate dehydrogenase in Escherichia coli

No abstract available

The purification of isocitrate dehydrogenase from Escherichia coli using immobilized dyes

No abstract available

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

Pyruvate metabolism and the phosphorylation state of isocitrate dehydrogenase in Escherichia coli

During growth of Escherichia coli on acetate, isocitrate dehydrogenase (ICDH) is partially inactivated by phosphorylation and is thus rendered rate-limiting in the Krebs cycle so that the intracellular concentration of isocitrate rises which, in turn, permits an increased flux of carbon through the anaplerotic sequence of the glyoxylate bypass. A large number of metabolites stimulate ICDH phosphatase and inhibit ICDH kinase in the wild-type (E. coli ML 308) and thus regulate the utilization of isocitrate by the two competing enzymes, ICDH and isocitrate lyase. Addition of pyruvate to acetate grown cultures triggers a rapid dephosphorylation and threefold activation of ICDH, both in the wild-type (ML308) and in mutants lacking pyruvate dehydrogenase (ML308/Pdh-), PEP synthase (ML308/Pps-) or both enzymes (ML308/Pdh- Pps-). Pyruvate stimulates the growth on acetate of those strains with an active PEP synthase but inhibits the growth of those strains that lack this enzyme. When pyruvate is exhausted, ICDH is again inactivated and the growth rate reverts to that characteristic of growth on acetate. Because pyruvate stimulates dephosphorylation of ICDH in strains with differing capabilities for pyruvate metabolism, it seems likely that pyruvate itself is a sufficient signal to activate the dephosphorylation mechanism, but this does not discount the importance of other signals under other circumstances

Amino acid sequence round the site of phosphorylation in isocitrate dehydrogenase from Escherichia coli ML308

Isocitrate dehydrogenase from Escherichia coli is regulated by a reversible phosphorylation mechanism. We report here the amino acid sequence round the phosphorylation site; this is the first such sequence to be reported for a bacterial protein kinase. The sequence does not resemble sequences phosphorylated by cyclic AMP‐dependent protein kinase