Purification and characterization of two thermostable cellulase-free xylanases from workers of the termite Macrotermes subhyalinus (Isoptera: Termitidae)

Abstract

Termite workers, Macrotermes subhyalinus (Rambur), produced two cellulase-free xylanases, namely Xyl A and Xyl B. DEAE-Sepharose CL-6B, Sephacryl S-200 HR, CM-Sepharose CL-6B and Phenyl-Sepharose CL-4B chromatographies purified these enzymes. They exhibited molecular masses of 63–66.1 (Xyl A) and 60.7–62.4 (Xyl B) kDa. Both enzymes appeared to be endo-xylanases, which produced oligomers of xylose from xylan and did not hydrolyse them to xylose. They had different optimum pH (pH 4.6–5.0 for Xyl A and pH 5.0 for Xyl B) and different optimum temperatures (60 °C for Xyl A and 55 °C for Xyl B). However, they had the same pH stability (4.0–5.6). Both enzymes were stable at 50 °C for more than 4 h. At a pH ranging from 4.6–5.0 and 60 °C, Xyl A and Xyl B possessed the half-life of 115 and 60 min, respectively. The xylanase activities were stimulated by Na+, Mn2+ and dithiol-reducing agents and were sensitive to Cu2+ and detergent agents. Their enzymatic activity was slightly reduced by the presence of urea at 1% (w/v) concentration. The two enzymes could be used in the presence of organic solvents such as acetone (up to 10% v/v) without loss of activity.