A new enzyme, maltobionate alpha-D-glucohydrolase, from alkalophilic Bacillus sp. N-1053

A new enzyme, maltobionate alpha-D-glucohydrolase, was purified to apparent homogeneity from a cell-free extract of alkalophilic Bacillus sp. N-1053 about 930-fold with a yield of 18% and some of its properties were investigated. The enzyme showed optimum activity at about pH 7.0, and was stable over the range of pH 6.0-9.5. The molecular weight was estimated to be 152,000 and 71,000 by HPLC gel filtration on TSKgel G3000SWXL and SDS-polyacrylamide gel electrophoresis, respectively. The enzyme hydrolyzed maltobionate more effectively than disaccharides such as maltose and maltitol or trisaccharides such as maltotrionate, maltotriose and maltotriitol, but showed no activity toward polysaccharides such as amylose, amylopectin and soluble starch. The reaction products from 1 mol of maltobionate were found to be 1 mol of beta-D-glucose and 1 mol of D-gluconate. The Km value for maltobionate was 1.63 mM and the Vmax/Km value for maltobionate was the largest among the substrates tested. The enzyme activity was almost completely inhibited by Hg2+, Ag+, iodine and N-bromosuccinimide, and also inhibited by p-nitrophenyl alpha-D-glucoside, maltose and maltitol.