Electrostatic facilitation of the reaction catalyzed by the manganese-containing and the iron-containing superoxide dismutases.

Both the iron-containing and the manganese-containing superoxide dismutases from Escherichia coli show diminished activity with increasing ionic strength, indicative of electrostatic facilitation of the catalyzed reaction. Since both enzymes bear a net negative charge at the assay pH, as does the substrate, this suggests a cationic locale in the active site region. Acetylation of the enzymes inverted their response to increasing ionic strength.

Electrostatic interactions in the reaction mechanism of bovine erythrocyte superoxide dismutase.

The activity of the copper- and zinc-containing superoxide dismutase decreased with increasing ionic strength. Modification of lysine residues by acetylation or succinylation inverted the effect of increasing ionic strength, whereas modification of arginine with phenylglyoxal did not. These results were noted in both photochemical and pulse-radiolysis assays.

Superoxide radical inhibits catalase.

Catalase was inhibited by a flux of O2- generated in situ by the aerobic xanthine oxidase reaction. Two distinct types of inhibition could be distinguished. One of these was rapidly established and could be as rapidly reversed by the addition of superoxide dismutase.

Oxygen toxicity in Streptococcus sanguis. The relative importance of superoxide and hydroxyl radicals.

Streptococcus sanguis, whose growth appears to be independent of the availability of iron, makes no hemes, contains neither catalase nor peroxidase, and can accumulate millimolar concentration levels of H2O2 during aerobic growth. It possesses a single manganese-containing superoxide dismutase whose concentration can be varied over a 50-100-fold range by manipulating the availability of oxygen during growth. Cell extracts contain a soluble NADH-plumbagin diaphorase which mediates O2- production in vitro and presumably also in vivo.

Manganese, superoxide dismutase, and oxygen tolerance in some lactic acid bacteria.

A previous study of the aerotolerant bacterium Lactobacillus plantarum, which lacks superoxide dismutase (SOD), demonstrated that it possesses a novel substitute for this defensive enzyme. Thus, L. plantarum contains 20 to 25 mM Mn(II),m in a dialyzable form, which is able to scavenge O2- apparently as effectively as do the micromolar levels of SOD present in most other organisms.

Chemistry and biochemistry of superoxide dismutases.

The univalent reduction of oxygen to the superoxide radical is a commonplace event in biological systems, and the superoxide dismutases, which catalytically scavenge this radical, are the primary defence against its potential cytotoxicity. The superoxide radical and hydrogen peroxide, can interact to generate the hydroxyl radical. Superoxide dismutases are metalloenzymes that can prevent the generation of hydroxyl radical by keeping the level of superoxide radical vanishingly low.

Manganese and defenses against oxygen toxicity in Lactobacillus plantarum.

Lactobacillus plantarum is aerotolerant during log-phase growth on glucose, but is an obligate aerobe on polyols. Respiration was cyanide resistant and under certain conditions was associated with the accumulation of millimolar concentrations of H(2)O(2). On glucose, optimal growth was observed in the absence of O(2).