PROBLEM TO BE SOLVED: To obtain the subject newα-glucosidase gene encoding a protein having a specific amino acid sequence and useful for producingα-glucosidase small in a Km value, excellent in substrate specificity and stability and used for measuring the activity ofα-amylase, etc. SOLUTION: This newα-glucosidase gene encodes a protein having an amino acid sequence of the formula or a protein having the amino acid sequence of the formula wherein one or more amino acids are deleted, replaced or added and having anα-glucosidase activity, and is used for efficiently producing anα-glucosidase small in a Km value, excellent in substrate specificity and stability, and useful as a coupling enzyme on the measurement of the activity ofα-amylase and on the determination of chloride ion or as an enzyme for determining or deleting maltooligosaccharide. The gene is obtained by cloning the chromosomal DNA of Bacillus s.p. KS-108a (FERM BP-5337).
