Purification and properties of three types of xylanases produced by an alkalophilic actinomycete

摘要

Three types of xylanases (l,4‐β‐D‐xylan xylanohydrolase, EC 3.2.1.8) were isolated from the culture filtrate of an alkalophilic actinornycete,Nocardiopsis dassonvilleisubsp.albaOPC‐18. The enzymes (X‐I, X‐II and X‐III) were purified by acetone precipitation, chromatographies of DEAE‐cellulofine A‐800, Sephadex G‐75 and preparative isoelectric focusing. The purified enzymes showed single bands on sodium dodecyl sulphate polyacrylamide gel electrophoresis. The molecular weights of X‐I, X‐II and X‐III were 23000, 23000 and 37000, respectively. The pIs were 4.9 (X‐I), 5.3 (X‐II) and 4.1 (X‐III). The optimum pH levels for the activity of X‐I and X‐II were pH 7.0. X‐III was also most active at pH 7.0, but 62.5 of the activity remained even at pH 11. The optimum temperatures for the activities of X‐I and X‐II were 60°C and that of X‐III was 50°C. X‐I and X‐II were stable in the range of pH 6–10, and X‐III wa