Abstract
The lipid hydrocarbon chains in the outer membrane of gram-negative bacteria appear from previous experiments to be less mobile than in the cytoplasmic membrane. To determine whether lipopolysaccharide, a unique outer membrane component, is a cause of this restricted mobility, outer membranes differing in the amount of lipopolysaccharide, and the length of the polysaccharide side chain, were prepared from Escherichia coli J5. Cytoplasmic membranes were prepared for comparison. The probes, 5- and 12-doxylstearate, were introduced into these membranes, electron spin resonance spectra were analyzed, and the order parameter (S) and empirical motion parameter (tau0) were calculated. Outer membrane preparations containing long chain lipopolysaccharide were much less fluid by these criteria than were preparations containing short chain lipopolysaccharide. Removing about 40% of the lipopolysaccharide from the former preparations greatly increased their fluidity. The lipid in the cytoplasmic membrane preparations was more fluid than in the outer membrane and cytoplasmic membranes were similar to each other regardless of the composition of the outer membrane. These results indicate that lipopolysaccharide, and especially the polysaccharide portion, directly or indirectly causes the restricted mobility of the lipid hydrocarbon chains observed in the outer membrane.
Highlights
Pharmacology, Metabolism, and Digestive Diseases, National Institutes of Health, School, The Hebrew University, National Institute ofArthritis, Bethesda, Maryland 20014
In the only reported experiments using membranes of defined lipid composition, Overath component, is a cause of this restricted mobility, outer et al [7] showed that inner and outer membranes of E. coli membranes differing in the amount of lipopolysaccharide, and the length of the polysaccharide side chain, were prepared from Escherichia coli 55
Outer membrane preparations containing long chain lipopolysaccharide were much less fluid by these criteria outer membrane, we have studied the effect of variations in lipopolysaccharide composition and content on the mobility of spin-labeled fatty acids in the outer membrane
Summary
Outer membrane preparations containing long chain lipopolysaccharide were much less fluid by these criteria outer membrane, we have studied the effect of variations in lipopolysaccharide composition and content on the mobility of spin-labeled fatty acids in the outer membrane. The lipid in the cytoplasmic membrane preparations was more fluid than in the outer membrane and cytoplasmic membranes were similar to each other regardless of the composition of the outer membrane These results indicate that lipopolysaccharide, and especially the polysaccharide portion, directly or indirectly causes the restricted mobility of the lipid hydrocarbon chains observed in the outer membrane. The outer membrane of gram-negative cells differs in many physiological and biochemical properties from the cytoplasmic membrane Their lipid content is similar, their proteins are totally different, and only the outer membrane contains lipopolysaccharide [1, 2].
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