Extracellular Maltase of Bacillus brevis

摘要

Bacillus brevis NRRL B-4389 produced extracellular maltase (α-glucosidase; EC 3.2.1.20) only in the presence of short α-1,4-glucosidic polymers, such as maltose and maltotriose. An optimum medium was developed; it contained 2.5% maltose, 0.5% nonfat dry milk, 0.4% yeast extract, and 0.01% CaCl2. The enzyme was produced extracellularly during the logarithmic phase of growth; no cell-bound activity was detected at any time. Partial purification of the maltase was accomplished by using diethylaminoethyl cellulose batch adsorption, ammonium sulfate precipitation, and Sephadex G-200 gel filtration. Maltase, isomaltase (oligo-1,6-glucosidase), and glucosyltransferase activities were purified 20.0-, 19.1-, and 11.5-fold, respectively. Some properties of the partially purified maltase were determined: optimum pH, 6.5; optimum temperature, 48 to 50°C; pH stability range, 5.0 to 7.0; temperature stability range, 0 to 50°C; isoelectric point, pH 5.2; and molecular weight, 52,000. The relative rates of hydrolysis of maltose (G2), maltotriose (G3), G4, methyl-α-d-maltoside, G40, dextrin, and isomaltose were 100, 22, 12, 10, 10, 8, and 5%, respectively; the Km on maltose was 5.8 mM; d-glucose, p-nitrophenyl-α-d-glucoside, and tris (hydroxymethyl) aminomethane were competitive inhibitors; transglucosylase activity of the enzyme on maltose resulted in the synthesis of isomaltose, isomaltotroise, and larger oligosaccharides.