a-Glucosidase 1 of Bacillus thermoamyloliquefaciens KPI 071 (FERM P8477, facultative thermophile) was purified to homogeneity. The relative molecular mass was estimated to be 62000 Da. From its catalytic properties, the enzyme has been assigned to an exo-a-1 ,4-glucosidase. The enzyme shares its antigenic groups in part with Bacillus stearotherrnophilus ATCC12016 (obligate thermophilc) exoa-1 ,4-glucosidase.These exo-a-1 ,4-glucosidases strikingly resemble oligo-l,6-glucosidases from B. thermoamyloliquefuciens KP1071 and from Bacillus cereus ATCC7064 in the molecular properties tested, including rclative 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-a-l,4-glucosidases take the same folded conformation, i.e. an (a/fl)8-barrel super-secondary structure in its N-terminal domain, as bacillary oligo-I ,6-glucosidases.A p-nitrophenyl-a-D-glucopyranosidase from Bacillus stemothcrmophilus ATCCl2016 (obligate thermophile) had been assigned to a novel exo-a-1,4-glucosidase [l]. However, no enzyme of similar function was found in othcr bacteria. Bacillus thrrmotrmyloIiquefuciens KP1071 (FERM P8477, facultative thermophile) produces a series of thermostable enzymes responsible for the complete hydrolysis of amylopectin, pullulan and cyclodextrin [2]. Of these enzymes, a maltotriogenic a-amylase I, a maltogenic a-amylase I1 capable of hydrolyzing a-1,6-bonds in amylopectin and of cleaving cyclodextrin rings, and an oligo-2,6-glucosidase have already been characterized [3 -51. However, serologically distinct a-glucosidases I, I1 and I11 at least remained to be isolated. In the present study, we have purified a-glucosidase 1 to homogeneity and assigned it to an exo-a-1,4-glucosidase. We have found a striking similarity of bacillary exo-a-l,4-glucosidases to bacillary oligo-I ,6-glucosidases in the N-terminal sequence and in structural parameters derived from the amino acid compositi on.