Purification and properties of extracellular alpha-glucosidase of a thermophile, Bacillus thermoglucosidus KP 1006

Abstract

An extracecular alpha-glucosidase (alpha-D-glucoside glycohydrolase, EC 3.2.1.20) of a thermophile, Bacillus thermoglucosidius KP 1006, was purified about 350-fold. The purified enzyme had a specific activity of 164 mumol of p-nitrophenyl-alpha-D-glucopyranoside hydrolyzed per min at 60 degrees C and pH 6.8 per mg of protein. The molecular weight was estimated at 55 000. The pH and temperature optima for activity were 5.0--6.0 and 75 degrees C, respectively. Below 40 degrees C, the activity was less than 4.5% of the optimym. The enzyme showed a high specificity for alpha-D-glucopyranoside. The maximal hydrolyzing velocity per substrate diminished in the order: phenyl-alpha-D-glucopyranoside, p-nitrophenyl-alpha-D-glucopyranoside, isomaltose, methyl-alpha-glycopyranoside. The respective Km values were 3.0, 0.23, 3.2 and 27 mM. The activity was trace for turanose, and not detectable for sucrose, trehalose, raffinose, melezitose, maltose, maltotriose, phenyl-alpha-D-maltoside, dextran, dextrin and starch. Tris, p-nitrophenyl-alpha-D-xylopyranoside, glucose and glucono-delta-lactone blocked competitively the enzyme with respect to p-nitrophenyl-alpha-D-glucopyranoside. The Ki values were 0.12, 0.14, 2.2 and 2.4 mM, respectively. The activity was affected by heavy metal ions, but insensitive to EDTA, p-chloromercuribenzoate and iodoacetate. The enzyme was stable up to 60 degrees C, and inactivated rapidly at temperatures beyond 72 degrees C. The pH range for stability was 4.0--11.0 at 31 degrees C, and 6.0--8.5 at 55.5 degrees C. At 25 degrees C, the enzyme failed to be inactivated in 45% ethanol, in 7.2 M urea, and in 0.06% sodium dodecyl sulfate, but the tolerance was extremely reduced at 60 degrees C.