Purification and Characterization of β-Amylase from Bacillus cereus BQ10-S1 Spo II

β-Amylase produced by Bacillus cereus BQ10-S1 Spo II was purified by salting out with ammonium sulfate, and column chromatography on Sephadex G-100 and CM-Sephadex C-50. The purified enzyme was homogeneous on disc electrophoresis and ultracentrifugation. Sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE) of the enzyme showed a single band suggesting no subunit structure. The sedimentation coefficient was 4.8S20,w and the molecular weight was estimated to be 6.0 × 104 by SDS-PAGE, 6.2 × 104 by gel filtration in the presence of 6 m guanidine HCl, 6.25 × 104 by sedimentation equilibrium and 5.5 × 104 by amino acid analysis, respectively. The Km value for soluble starch was 0.4%. The enzyme was remarkably inhibited by 5 × 10−9 m PCMB but not by DTNB at the same concentration. Only one sulfhydryl group was detected by amino acid analysis, by Elluman′s and Riordan′s methods. The isoelectric point of the purified enzyme was 8.3.