Maltotriose-producing Amylase from Microbacterium imperiale

A maltotriose-producing amylase, which hydrolyzes the α-1,4-glucosidic linkages in starch with maltotriose units was found in the culture filtrate of a strain of the genus Microbacterium newly isolated from soil. The enzyme was purified almost to homogeneity by ammonium sulfate fractionation, DEAE-Sepharose column chromatography and Sephadex G-150 column chromatography. Its optimum pH and temperature were around 6.5–7.0 and around 50°C, respectively. The enzyme was protected from heat in the presence of calcium ion. Its molecular weight was estimated to be about 40,000 by the gel filtration method. Typical sugar composition of hydrolysis products from liquefied starch was about 55–60% of maltotriose, 10–20% of maltose, 1–3% of glucose and 20–40% of other higher oligosaccharides.