A pH titration study on the ionic bridging within lipopolysaccharide aggregates

Richard T. Coughlin, Arnold A. Peterson, A. Haug, Henry J. Pownall, Estelle J. McGroarty

Research output: Contribution to journalArticlepeer-review

35 Scopus citations


The packing of lipopolysaccharide aggregates from rough strains of Escherichia coli was examined at different pH values. Lipopolysaccharide head-group motion, measured with an electron spin resonance probe, was found to be dependent on pH, and indicated the existence of multiple ionizable groups. Lipopolysaccharide from a rough (Ra) and a heptose-less (Re) mutant were more rigid at pH 5 than at pH 10.5. In addition, head-group mobility of the magnesium salt of Ra lipopolysaccharide was substantially less than that of the sodium salt at pH 7.0, whereas at high pH (pH 12) the two salts were equally fluid. Changes in head-group packing were also reflected in pH-dependent changes in the phase transition measured with differential scanning calorimetry. The enthalpy of the transition, ΔHt, for the sodium salt of Re lipopolysaccharide was greatest at pH 7.5 and approached zero in both the acidic and the basic pH ranges. We propose that fixed charges in the core and lipid A regions significantly influence lipopolysaccharide head-group motion and the lipopolysaccharide aggregation state. Furthermore, ionic bridging among phosphate groups dramatically rigidifies head group interactions in the neutral to acidic pH ranges.

Original languageEnglish (US)
Pages (from-to)404-412
Number of pages9
JournalBBA - Biomembranes
Issue number3
StatePublished - Dec 19 1985


  • (E. coli)
  • Differential scanning calorimetry
  • ESR
  • Headgroup mobility
  • Lipopolysaccharide
  • pH dependence
  • Phase transition

ASJC Scopus subject areas

  • Cell Biology
  • Biophysics
  • Biochemistry
  • Medicine(all)


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