Thermostable α-glucosidase produced by Bacillus caldovelox DSM411

Abstract

Bacillus caldovelox produces an intracellular α-glucosidase (EC 3.2.1.20). It is the most thermostable microbial α-glucosidase reported to date and a number of its properties are outlined here. It was purified by treatment with protamine sulphate and gel filtration on Sephadex G-150 and gave a single band on SDS–PAGE. The enzyme had highest activity on p-nitrophenyl-α-D-glucoside, which was 2.04 times higher than the activity on maltose, and it was inactive towards isomaltose. It had a molecular weight of 30 000 and an isoelectric point of pH 5.0. The enzyme operated most efficiently at pH 5.5–6.0 and at 50–60 °C. It possessed considerable pH stability, retaining 80% or more activity in the range pH 4.0–9.0. α-Glucosidases tend to be very unstable, but this enzyme was fully stable up to 60 °C for 1 h and retained 51% of its original activity on incubation at 70 °C over the same period. The presence of histidine, cysteine, and manganous ions improved the thermal stability of the enzyme considerably. EDTA, α,α′-dipyridyl, o-phenanthroline, barium, strontium, manganous ions, and glucose stimulated activity, while Tris, ribose, glucono-δ-lactone, and phenyl-α-D-glucoside inhibited activity.