Purification and Characterization of an Oligo‐1,6‐glucosidase from the Caldoactive Thermophile Bacillus caldotenax

Abstract

AbstractAn oligo‐1,6‐glucosidase (dextrin 6‐α‐D‐glucanhydrolase, EC 3.2.1.10) of the caldoactive thermophile Bacillus caldotenax KP 1213 (YT‐G, DSM406) was purified to homogeneity. Its relative molecular weight, Stokes radius, sedimentation coefficient at 20°C in water, molar absorption coefficient at 280nm and pH 6.8, and isoelectric point were estimated to be 64,000, 3.3nm, 4.8S, 122,000M−1cm−1, and 4.9, respectively. The enzyme N‐terminal sequence of twenty residues was determined to be Met1‐Glu‐Trp‐Ala‐Trp‐Lys‐Glu‐Ala‐Val‐Val‐Tyr‐Gln‐Ile‐Tyr‐Pro‐Arg‐Met‐Phe‐Tyr20. The enzyme shared its antigenic groups in part with the homologue from Bacillus thermoglucosidasius KP1006 (DSM2542, obligate thermophile). The B. caldotenax enzyme was most active at 70°C and at pH 6.0–6.8. The best substrate for the enzyme was isomaltotriose of naturally‐occurring oligo‐ and polysaccharides tested. The enzyme half‐life at pH 6.8 was 10min at 75°C. The enzyme (Pro, 5.93mol%) fairly matched with a positive relationship between the thermostability of its six bacillary counterparts and their proline mol% contents. This relationship has been found to hold for sixteen bacterial enzymes from other four different groups (α‐glucosidases, pullulanases and 3‐isopropylmalate dehydrogenases).