Physicochemical Studies on a Lipopolysaccharide from the Cell Wall of Azotobacter vinelandii

Abstract

Abstract Lipopolysaccharide prepared from the cell wall of Azotobacter vinelandii was found to consist of two polydisperse components: s20 = 8 to 16 S and s20 = 70 to 100 S. Treatment of this material with ethylenediaminetetraacetate resulted in dissociation into a smaller homogeneous unit with a molecular weight of 134,000 daltons. Subsequent dialysis in the presence of CaCl2 produced a reassociated polymer with a molecular weight of 873,000 daltons. Dissociation of the lipopolysaccharide was also effected by dodecyl sulfate. The smallest subunit, obtained by the combined action of dodecyl sulfate and ethylenediaminetetraacetate, had a molecular weight of 65,600 daltons when corrected for binding of dodecyl sulfate. Equilibrium and velocity sedimentation and viscosity measurements characterize both the dissociated and reassociated species as relatively homogeneous, highly asymmetric particles. The hydrogen ion titration curve has clearly identifiable segments due to the titration of carboxyl and amino groups. The latter appear to have a lower intrinsic pK than expected from the partially known structure. The lipopolysaccharide was shown to contain phosphate, glucose, and a 2-keto-3-deoxy sugar. Ribose, rhamnose, and hexosamine were identified tentatively.