Lethal Synthesis of Methylglyoxal by Escherichia coli During Unregulated Glycerol Metabolism

Abstract

In Escherichia coli K-12, the conversion of glycerol to triose phosphate is regulated by two types of control mechanism: the rate of synthesis of glycerol kinase and the feedback inhibition of its activity by fructose-1,6-diphosphate. A strain which has lost both control mechanisms by successive mutations, resulting in the constitutive synthesis of a glycerol kinase no longer sensitive to feedback inhibition, can produce a bactericidal factor from glycerol. This toxic factor has been identified by chemical and enzymological tests as methylglyoxal. Methylglyoxal can be derived from dihydroxyacetone phosphate through the action of an enzyme which is present at high constitutive levels in the extracts of the mutant as well as that of the wild-type strain. Nine spontaneous mutants resistant to I mm exogenous methylglyoxal have been isolated. In all cases the resistance is associated with increased levels of a glutathione-dependent enzymatic activity for the removal of methylglyoxal. Methylglyoxal-resistant mutants derived from the glycerol-sensitive parental strain also became immune to glycerol.

The role of glyoxalase I in the detoxification of methylglyoxal and in the activation of the KefB K+ efflux system in Escherichia coli

“…Thus, the synthesis of MG requires low phosphate and high DHAP, a situation that most frequently pertains when either glucose flux exceeds the potential for growth (Hopper and Cooper, 1971) or, in E. coli, during growth on some carbon sources in the presence of cAMP (Ackerman et al, 1974). Mutants deregulated for glycerol metabolism also form MG when grown on this carbon source (Freedberg et al, 1971). Accumulation of MG to approximately 300 M can cause growth arrest, and higher concentrations cause cell death (Ferguson et al, 1996).…”

From famine to feast: the role of methylglyoxal production in Escherichia coli

“…The toxicity is still poorly understood at the molecular level, but this electrophile has the capacity to modify DNA and proteins leading to inactivation of cells (Krymkiewicz et al, 1971;Lo et al, 1994;Papoulis et al, 1995). Escherichia coli cells, stimulated to produce MG by deregulation of the transport and metabolism of glucose-6-phosphate, arabinose, gluconate, glycerol and xylose, rapidly lose viability (Freedberg et al, 1971;Rekarte et al, 1973;Ackerman et al, 1974;Kadner et al, 1992). Growth inhibition is usually observed when MG passes a threshold concentration of 0.3 mM, and cell death occurs once the external concentration exceeds 0.6 mM (Ferguson et al, 1996).…”

A novel aldo-keto reductase from Escherichia coli can increase resistance to methylglyoxal toxicity

“…One of these, methylglyoxal, is a biologically active dicarbonyl that is known to be produced by a range of microorganisms, including E. coli [252 7]. Because of its reactive carbonyl groups, it causes damage to DNA and protein [28,29], leading to loss of viability [25,30]. In E. coli, detoxi¢cation of methylglyoxal has been demonstrated previously through two related routes: (1) the activation of K þ channels KefB and KefC by a methylglyoxal^glutathione conjugate which leads to cytoplasmic acidi¢cation that protects against the electrophile [31]; and (2) metabolism of methylglyoxal^glutathione conjugates via glyoxalase I and II to D-lactate and glutathione [26,32].…”

“…To characterise the enzyme further, apparent kinetic constants were determined for those substrates for which YghZ had highest speci¢c activity ( Table 2). The a⁄nity for methylglyoxal (K m = 3.24 mM) suggests it could function to reduce methylglyoxal over the range of physiological levels found within the cell (up to 1.4 mM) [25].…”