Regulation of acetyl coenzyme A synthetase in Escherichia coli

Cells of Escherichia coli growing on sugars that result in catabolite repre ssion or amino acids that feed into glycolysis undergo a metabolic switch a ssociated with the production and utilization of acetate. As they divide ex ponentially, these cells excrete acetate via the phosphotransacetylase-acet ate kinase pathw ay. As they begin the transition to stationary phase, they instead resorb acetate, activate it to acetyl coenzyme A (acetyl-CoA) by m eans of the enzyme acetyl-CoA synthetase (Acs) and utilize it to generate e nergy and biosynthetic components via the tricarboxylic acid cycle and the glyoxylate shunt, respectively. Here, we present evidence that this switch occurs primarily through the induction of acs and that the timing and magni tude of this induction depend, in part, on the direct action of the carbon regulator cyclic AMP receptor protein (CRP) and the oxygen regulator FNR. I t also depends, probably indirectly, upon the glyoxylate shunt repressor Ic lR, its activator FadR, and many enzymes involved in acetate metabolism. On the basis of these results, we propose that cells induce acs, and thus the ir ability to assimilate acetate, in response to rising cyclic AMP levels, falling oxygen partial pressure, and the flux of carbon through acetate-ass ociated pathways.