Some studies of the regulation of gluconeogenesis in enterobacteriacae.

The pathway and regulation of the gluconeogenic conversion of pyruvate to glyceraldehyde 3-phosphate (G3P) and dihydroxyacetone phosphate (DHAP) in Escherichia coli K12 and Salmonella typhimurium LT2 has been investigated. It has been shown that the conversion of pyruvate to phosphoenol-pyruvate (PEP) in S.typhimurium LT2 is catalysed by the enzyme PEP synthetase. Three genes involved in the synthesis of this enzyme have been identified. One of these genes (PPSA), situated at approximately minute 46 of the S. typhimurium chromosome linkage map appears to be a structural gene for PEP synthetase, whilst the ppsB and ppsC genes, situated at approximately minute 46 and minute 3 respectively of the S. typhimurium chromosome linkage map appear to have a regulatory function. Possible models to explain the control of PEP synthetase formation in S. typhimurium LT2 are discussed and it appears likely that the synthesis of this enzyme is subject to a positive control type of regulation, analogous to the regulation of the synthesis of the maltose catabolising enzymes of E. coli. E. coli K12 3-phosphoglycerate kinase has been studied and shown to be subject to control by the adenylate energy charge, when assayed in the gluconeogenic direction. Little or no effect of energy charge on the activity of this enzyme was seen when the enzyme was assayed in the glycolytic direction. Some kinetic properties of this enzyme have been investigated and the physiological significance of adenylate energy charge control is discussed. Evidence is also presented for a new reaction involved in bacterial gluconeogenesis. This enzyme appears to catalyse a gluconeogenic reaction between PEP and the triose phosphates DHAP and G3P, possibly at a step after 3-phosphoglycerate. Mutants have been isolated which, unlike the parental strain, are able to synthesise this novel enzyme after growth on gluconate or a mixture of 25mM pyruvate plus 10mM glucose.