Some aspects of carbohydrate metabolism.

Mutants of Escherichia coli with defects in triose phosphate isomerase (il.;i"), fructose diphosphate (FDP) aldolase(Fda") and pentose metabolism were used to investigate the role of glyceraldehyde 3-phosphate (G 3-.;) and dihydroxy ace tone phosphate (DHAP) in gluconeogenesis.A block in gluconeogenesis prevented growth of Q.;i -mutants on non-carbohydrates.Studies on glycogen synthesis suggested that both G and DHAP were required for the formation of the hexose moiety in gluconeogenesis. To explain the ability of Tpi -mutants to synthesize glycogen from glycerol, a novel route for the conversion of DHAP to G 3-P involving methyl glyoxal has been proposed. Both d.;i" and !I.;i.;strains of E. coli possessed an enzyme which convertedDHAP to methyl glyoxal. When the !I.;i"-mutants were exposed to compounds whichwere catabolized to DHAP, this accumulated and methyl glyoxal was excreted into the medium. Studies on gluconate and carbohydrate metabolism suggested that the impaired growth of Tpi - mutants on certain carbohydrates may be due to a deficiency in phosphoenolpyruvate and inhibition of glycolysis. The gene specifying triose phosphate isomerase was highly cotransducible with that for 6-phosphofructokinase. The presence of a small amount of aldolase in Fda -mutants probably explained their gluconeogenic ability. This enzyme showed a hi.;er ratio for FDP synthesis to FDP cleavage activity than the FDPaldolase in the parental strains. Further studies on FI3P cleavage activity shov;ed that these enzymes also differed in the pH-activity profile, the degree of activation by divalent metal ions and thiols and the K and V values m max A deficiency in idbose permease for one mutant and ribokinase for another, prevented their growth on ribose. CEhe chromosomal location of the gene specifying ribokinase was close to that for ribose permease.