A teichuronic acid, containing glucuronic acid and N-acetylgalactosamine, was purified from acid extracts of Bacillus licheniformis 6346 cell walls as described by Janczura, Perkins & Rogers (1961). After reduction of the carboxyl function of glucuronic acid residues in the polysaccharide the reduced polymer contains equimolar amounts of N-acetylgalactosamine and glucose. Methylation of the reduced polysaccharide by the Hakamori (1964) technique showed the glucose residues to be substituted on C-4. A disaccharide, 3-O-glucuronosylgalactosamine, was isolated from partial acid hydrolysates of teichuronic acid. After N-acetylation the disaccharide produces chromogen readily on heating at pH7, in agreement with C-3 substitution of the reducing N-acetylamino sugar. Teichuronic acid also produces chromogen under the same conditions, with concurrent elimination of a modified polysaccharide from C-3 of reducing terminal N-acetylgalactosamine residues of the teichuronic acid chains. The number-average chain lengths of several preparations of teichuronic acid were estimated from the amounts of chromogen produced in comparison with the N-acetylated disaccharide. The values obtained are in good agreement with the weight-average molecular weight determined by ultracentrifugal analysis. The reducing terminals of teichuronic acid are shown to be exclusively N-acetylgalactosamine by reduction with sodium boro[3H]hydride. The number-average chain lengths of the teichuronic acid preparations were estimated by the extent of in corporation of tritium and are in agreement with values obtained by the other methods.

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