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Abstract:
Lipopolysaccharide (LPS) of a number of gram-negative bacteria affected mitochondrial respiration and phosphorylation when it was preincubated with the mitochondrial suspension. The structural part responsible for this activity of LPS is the lipid moiety (lipid A), because the lipid A prepared from either the LPS of Escherichia coli or the endotoxic glycolipid of a heptose-less mutant (R595) of Salmonella minnesota affected mitochondrial oxidative phosphorylation as did LPS, whereas the polysaccharide moiety was inactive. Preincubation of the mitochondrial suspension with lipid A resulted in (i) inhibition of respiration and accompanying phosphorylation in the presence of either succinate or a number of reduced nicotinamide adenine dinucleotide-linked substrates, (ii) decrease of respiratory control, (iii) inhibition of the transfer of electrons at coupling site II without decrease of efficiency of phosphorylation, and the uncoupling at coupling site III, and (iv) stimulation of adenosine triphosphatase and the inhibition of 2,4-dinitrophenol-induced adenosine triphosphatase.
Insights
Lipopolysaccharide (LPS) from gram-negative bacteria impairs mitochondrial respiration and phosphorylation. The lipid A component, not the polysaccharide, is responsible for this inhibitory effect on oxidative phosphorylation.
Area of Science:
- Biochemistry
- Cell Biology
- Microbiology
Background:
- Gram-negative bacteria produce lipopolysaccharide (LPS), a potent endotoxin.
- LPS is known to elicit strong immune responses and can have toxic effects.
Purpose of the Study:
- To investigate the specific component of LPS responsible for its effects on mitochondrial function.
- To elucidate the mechanism by which LPS impacts mitochondrial respiration and phosphorylation.
Main Methods:
- Mitochondrial suspensions were preincubated with purified lipopolysaccharide (LPS) and its components.
- Mitochondrial respiration, phosphorylation, respiratory control, and ATPase activity were measured.
- Electron transfer at specific coupling sites was analyzed.
Main Results:
- Lipopolysaccharide (LPS) inhibited mitochondrial respiration and phosphorylation.
- The lipid A moiety of LPS, but not the polysaccharide, was responsible for the observed effects.
- Lipid A decreased respiratory control, inhibited electron transfer at coupling site II, and caused uncoupling at coupling site III.
- Lipid A stimulated ATPase activity and inhibited 2,4-dinitrophenol-induced ATPase activity.
Conclusions:
- The lipid A component of LPS is the primary driver of mitochondrial dysfunction.
- LPS disrupts mitochondrial oxidative phosphorylation through multiple mechanisms, including effects on electron transport and ATP hydrolysis.
- These findings highlight the direct impact of bacterial endotoxins on cellular energy production.