Characterization of meningococcal polysaccharides by optical mixing spectroscopy. II. Effects of temperature, EDTA, and ionic strength on aggregation of group C polysaccharides in solution

O-acetylation affects the binding properties of the carboxyl groups on the Vi bacterial polysaccharide

The capsular polysaccharide of Salmonella typhi and Citrobacter freundii (Vi) is a linear homopolymer of (1-->4)-linked 2-acetamido-2-deoxy-alpha-D-galactopyranosyluronic acid partially O-acetylated at the C-3 position. The physico-chemical properties of the carboxyl groups of the Vi polysaccharide, as a function of different degrees of O-acetylation, were studied by potentiometric titration, circular dichroism, and their reaction with the bulky nucleophile 2-nitro-phenylhydrazine (NPH). Potentiometric titrations with K+ and Ca2+ hydroxides showed that the difference in the free energy of binding between the two cations (delta GKCa) was inversely proportional to the degree of O-acetylation. Similar cationic effects were found when measuring circular dichroism. Moreover there was also an inverse relation between the degree of O-acetylation and the extent of binding of NPH to the carboxyl groups. These data all indicate that O-acetyl groups hinder the association of carboxyls with cations and nucleophilic reagents. This provides a possible explanation for the importance of the O-acetyl and the relative unimportance of the carboxyl groups in contributing to the immunologic properties of the Vi.

Analysis of the chain length of oligomers and polymers of sialic acid isolated from Neisseria meningitidis group B and C and Escherichia coli K1 and K92

A series of (2----8)-alpha-, (2----9)-alpha-, and alternate (2----8)-alpha- and (2----9)-alpha-linked oligomers of sialic acid (N-acetylneuraminic acid, NeuNAc) was prepared by digestion with bacteriophage or by partial hydrolysis at pH 7.0 and 100 degrees of polymers of sialic acid produced by Neisseria meningitidis and Escherichia coli. The oligosaccharides were purified by gel filtration or by anion-exchange chromatography, and their chain lengths were determined by colorimetric measurement of the formaldehyde released from the non-reducing end residue after periodate oxidation, radiolabelling of the reducing end residue by reduction with borotritiide, and determination of the ratio of the non-reducing end and internal residues by g.l.c. of the trimethylsilyl derivatives of the methyl ester methyl beta-ketosides. 1H-N.m.r. spectroscopy was used to confirm the chain length of two oligosaccharides. These methods were used to determine the average chain-length of the sialic acid polysaccharides produced by N. meningitidis and E. coli and the percentage of chains with covalently bound lipid moieties at the reducing end.

Electron microscopical study of Neisseria meningitidis releasing various amounts of free endotoxin

A study has been made of the ultrastructure of four strains of Neisseria meningitidis which liberate varying amounts of free endotoxin in a chemically-defined, protein-free medium. The two strains which did not release detectable or only sparse amounts of free, filtrable endotoxin were rather uniform in cell size. Their cells appeared to be intact and showed a low tendency to aggregate, In addition cells of these strains showed only sporadic loose, trilaminar membranes and blebs, and free membranous structures were sparse in the medium. The endotoxin releasing strains liberated a high yield of free structures from the outer cell wall into the medium. These structures may represent the lipopolysaccharide (LPS).