Three extracellular /?-mannanases (M-I, M-II, and M-III) of an alkalophilic Bacillus sp. (AM-001) were purified to an electrophoretically homogenous state. Molecular weights and pi values of the purified enzymes (M-I, M-II, and M-III) were 58,000, 59,000, and 42,000 by SDS-PAGE and 5.9, 5.7, and 5.1 by isoelectric focusing, respectively. These enzymes were most active at pH 9.0 and 60°C (M-I and M-II) and pH 8.5 and 65°C (M-III). The enzymes were activated slightly by cysteine, and -inhibited strongly by Ag+ and N-bromosuccinimide. Michaelis constants (Km) of the M-I enzyme for /?-mannans from copra, locust bean, and konjak were 2.0, 3.8, and 7.7mg/ml, and maximum velocities (Vm. dx) for these saccharides were 730, 1470, and 1880U/mg-protein, respectively. The kinetic properties of M-II and M-III enzymes were almost the same as those of M-I. About 22, 16, 15, and 2:5% of the /M,4-mannosidic linkages in ^-mannans from copra, konjak, locust bean, and guar bean were hydrolyzed by the M-I enzyme, and the major components in the digests were di-, tri-, and tetra-saccharides. These enzymes hydrolyzed /M,4-mannooligosaccharides larger than mannotriose.
