Xanthan Lyases - Novel Enzymes Found in Various Bacterial Species

SUMMARY: Xanthan lyases, cleaving the terminal β-mannosidic linkage of the side-chain of the exopolysaccharide xanthan from Xanthomonas campestris, have been obtained from several sources. These include a Bacillus species, a Corynebacterium species and a mixed culture. The lyases were initially associated with endo-β-glucanases cleaving the main chain of xanthan. Partial purification of the enzymes was achieved and the Bacillus preparation was separated by FPLC into material free of endoglucanase and glycosidase activities. The lyase was active on polysaccharides with and without acetate and pyruvate. The optimal size of the substrate appeared to be in the range of degree of polymerization (DP) 25–35, i.e. 5–7 repeat units of the polysaccharide. No activity was found against xanthan modified by reduction of the carboxyl groups or by the addition of amine or hydroxyethyl groups. The combined action of the lyase and the endoglucanase yielded a series of oligosaccharides, each with a side-chain terminating in an unsaturated uronic acid and containing the molar ratio of d-glucose to d-mannose, 2:1.