Requirements of acetyl phosphate for the binding protein-dependent transport systems in Escherichia coli

In Escherichia coli, acetyl phosphate can be formed from acetyl-CoA via the phosphotransacetylase (phosphate acetyltransferase; acetyl-CoA:orthophosphate acetyltransferase, EC 2.3.1.8) reaction and from acetate (plus ATP) via the acetate kinase (ATP:acetate phosphotransferase, EC 2.7.2.1) reaction. By restricting acetyl phosphate formation to the phosphotransacetylase reaction alone, through the use of metabolic inhibitors, we were able to show that, with pyruvate as a source of energy, mutants defective in phosphotransacetylase are unable to transport glutamine, histidine, and methionine. However, with the same energy source, mutants defective in acetate kinase are normal in the transport of these amino acids. The inability of the phosphotransacetylase mutants to transport is due to their presumed inability to form acetyl phosphate, because pyruvate is found to be metabolized to acetyl-CoA in these mutants. Thus acetyl phosphate has been implicated in active transport. Evidence is also presented that neither the protonmotive force nor the ecf gene product is required for the shock-sensitive transport systems.