Superoxide Dependence of the Toxicity of Short Chain Sugars

Abstract

Erythrose inhibited the growth of a sodA sodB strain of Escherichia coli under aerobiosis; but did not inhibit anaerobic growth of the sodA sodB strain, or the aerobic growth of the superoxide dismutase (SOD)-competent parental strain. A SOD mimic protected the sodA sodB strain against the toxicity of erythrose as did the carbonyl-blocking reagents hydrazine and aminoguanidine. Three carbon sugars, such as glyceraldehyde and dihydroxy acetone, and the two carbon sugar glycolaldehyde, were similarly toxic in an O 2 . -dependent man-ner. An unidentified dialyzable component in E. coli extract augmented the oxidation of short chain sugars, and this was partially inhibitable by SOD. The toxicity of the short chain sugars appears to be because of an O 2 . -dependent oxidation to ␣,␤-dicarbonyl compounds.In keeping with this view was the O 2 . -independent toxicity of methylglyoxal.We have previously noted that ␣-hydroxycarbonyl compounds can autoxidize with the production of O 2 .(1). Cyanide, and to a lesser extent other nucleophiles, strongly accelerated this autoxidation, and the augmenting effect of preincubation at elevated pH indicated the involvement of an enediolate intermediate. This cyanide-catalyzed oxidation had been seen earlier with methylglyoxal (2, 3). Oxidation of ␣-hydroxycarbonyl compounds was subsequently seen to proceed as a chain reaction in which O 2 . could serve as both an initator and a propagator (4). The autoxidation of such compounds have been studied by others, who also noted O 2 . production (5, 6) and the role of enolization (5). ␣-Amino carbonyl compounds appear to behave in a similar way (7-9). The mutagenicity of ␣-hydroxycarbonyl compounds in Salmonella typhimurium was attributed to their ease of autoxidation with attendant oxy radical production (10). During an attempt to use erythrose as a carbon source for the growth of a sodA sodB strain of Escherichia coli, we noted an oxygen-dependent toxicity and set out to explore its mechanism. The data reported herein indicate a role for O 2 . in the toxicities of erythrose and shorter chain sugars. These results are relevant to the much slower process of nonenzymic glycation seen with long chain sugars, such as glucose, which exist primarily as internal hemiacetals and are therefore less reactive (11-15). MATERIALS AND METHODSD(Ϫ)-Erythrose was from Fluka, whereas aminoguanidine and methylglyoxal were obtained from Aldrich. DL-Glyceraldehyde, glycolaldehyde, dihydroxy acetone, and the phosphate esters of glyceraldehyde, erythrose, and dihydroxy acetone, were from Sigma. The strains of E. coli used in these studies were AB1157, which was the parental strain for JI132 that was sodA sodB (16). Starter cultures were usually grown overnight in aerobic LB medium at 37°C and were then diluted 200-fold into M9CA medium. LB and M9CA were as described (17). Anaerobiosis, when desired, was achieved in Gas Pack jars. These jars were opened at intervals to allow turbidimetry, following which the jars were evacuated and refilled with N 2 . Culture gro...

Escherichia coli aconitases and oxidative stress: post-transcriptional regulation of sodA expression

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Why Superoxide Imposes an Aromatic Amino Acid Auxotrophy onEscherichia coli

“…Moreover a dimerization reaction would proceed even less well when the concentration of the monomer was very low. We have noted a toxicity of short chain sugars and have related it to the reactivity of the exposed carbonyl group and to the formation of enediolate tautomers, which can oxidize to very toxic ␣-␤ diketones (32). Hence short chain sugars should be kept at vanishingly low concentrations to prevent this.…”

Regulatory and Structural Differences in the Cu,Zn-Superoxide Dismutases of Salmonella enterica and Their Significance for Virulence

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