Studies on Bacillus licheniformis endo-\-1,3-1,4-d-glucanase: characterization and kinetic analysis

A new purification procedure for endo-\-1,3-1,4-d-glucanase from Bacillus licheniformis is described. The secreted enzyme was purified both from B. licheniformis and from recombinant Escherichia coli harbouring the cloned gene by ion exchange chromatography on a CM-Sepharose matrix at pH 5.6. The mature enzyme was resistant to proteolysis by trypsin and chymotrypsin but it was slowly digested by protease V8. It showed a continuous trimming where no large-limit polypeptides were noticeable thus supporting a monodomain structure. Former appearing peptides have been assigned theoretically according to the protein sequence and predictive methods of accessible areas. Kinetic parameters for the hydrolysis of barley \-glucan and lichenan by measuring the net release of reducing sugars at the optimum pH (7.02) and temperature (55° C) are k_cat=3500 ±800 s^-1 (turnover number) and K_m=1.45±0.21 mg/ml for barley \-glucan and k_cat=3000±750 s^-1 and K_m=1.98±0.40 mg/ml for lichenan.