Assignment of Bacillus thermoamyloliquefaciens KP1071 alpha-glucosidase I to an exo-alpha-1,4-glucosidase, and its striking similarity to bacillary oligo-1,6-glucosidases in N-terminal sequence and in structural parameters calculated from the amino acid composition.

alpha-Glucosidase I of Bacillus thermoamyloliquefaciens KP1071 (FERM P8477, facultative thermophile) was purified to homogeneity. The relative molecular mass was estimated to be 62,000 Da. From its catalytic properties, the enzyme has been assigned to an exo-alpha-1,4-glucosidase. The enzyme shares its antigenic groups in part with Bacillus stearothermophilus ATCC12016 (obligate thermophile) exo-alpha-1,4-glucosidase. These exo-alpha-1,4-glucosidases strikingly resemble oligo-1,6-glucosidases from B. thermoamyloliquefaciens KP1071 and from Bacillus cereus ATCC7064 in the molecular properties tested, including relative molecular mass, N-terminal sequence of 15 residues, amino acid composition and structural parameters calculated from amino acid composition. We have suggested that bacillary exo-alpha-1,4-glucosidases take the same folded conformation, i.e. an (alpha/beta)8-barrel super-secondary structure in its N-terminal domain, as bacillary oligo-1,6-glucosidases.