Metabolism of L-glyceraldehyde 3-phosphate in Escherichia coli

E. coli is able to incorporate L-glyceraldehyde and L-glyceraldehyde 3-phosphate into phospholipids, L-[3-3H]Glyceraldehyde was synthesized and the purity and the chemical identity of the product were checked by paper chromatography. L-[3-3H]Glyceraldehyde 3-phosphate was synthesized from L-[3-3H]glyceraldehyde in a reaction catalyzed by glycerokinase. E. coli extract contains a new enzyme activity which catalyzes an NADPH dependent reduction of L-glyceraldehyde 3-phosphate into sn-glycerol 3-phosphate. A procedure, specifically suitable for assaying the reductase activity in the crude extract, was developed. A more convenient spectrophotometric assay method was employed for the purified enzyme. At moderate concentrations sulfhydryl group inhibitors had no effect on the enzyme activity of L-GAP reductase. At 100μM concentration Zn+2 inhibited the enzyme activity by about 30% while Mn+2 elevated the activity by about the same margin. Mg+2, Ca+2 and Fe+2 were without effect at this concentration. L-Glyceraldehyde 3-phosphate is known to be bactericidal at 1.25 μM concentration and the D-enantiomer is without effect. Furthermore, methylglyoxal is known to be bactericidal at or above 0.5 mM concentration. Strains of E. coli resistant to 1 mM methylglyoxal were isolated. The cell extract prepared from the mutant possessed increased capacity to transform methylglyoxal into D-lactate via a glutathione dependent reaction. These mutants were less sensitive to 2.5 mM DL-GAP suggesting that conversion of L-glyceraldehyde 3-phosphate into methylglyoxal may at least partly be responsible for the bactericidal activity of L-GAP