Purification and characterization of a novel lichenase from Bacillus licheniformis GZ-2

摘要

A novel lichenase from Bacillus licheniformis GZ-2 was purified to homogeneity by two steps ion-exchange chromatography with a specific activity of 8231.3U/mg. The purified enzyme showed as a single protein band with a molecular mass of 25 kDa. The optimum pH and temperature for the enzyme activity were 6.5 and 60 degrees C, respectively. The enzyme exhibited strict specificity for -1,3-1,4-d-glucans. The kinetic parameters K-m and V-max were 5.11mg/mL and 2097 mu mol/Min/mg for lichenan and 7.42mg/mL and 1440 mu mol/Min/mg for barley -glucan. Compared to most of the reported -1,3-1,4-glucanases (lichenase), the activity of the purified enzyme for lichenan was much higher than that for barley -glucan. The main products of -glucan hydrolyzed by the lichenase were cellubiosyltriose (DP3) and cellutriosyltraose (DP4). The lichenase gene from B.licheniformis GZ-2 was cloned and sequenced. The open reading frame of gene gz-2 contained 642 bp coding for a 214 amino acid mature protein. The gene was cloned into an expression vector pET 28a and expressed in Escherichia coli BL21. The activity in cell lysate supernatant was 137.9U/mg.