Characterization of Pullulanase and α‐Amylase Activities of a <i>Thermus</i> sp. AMD33

Abstract

Abstract Thermostable Thermus sp. AMD 33 pullulanases (I and II) capable of cleaving α‐1,6‐links in pullulan as well as α‐1,4‐glucosidic linkages in amylose were purified to electrophoretically homogeneous states. Relative molecular masses and pI values were determined as 135,000 (I and II) by SDS‐PAGE and 4.2 (I) and 4.3 (II) by isoelectric focusing, respectively. The pullulanase and α‐amylase activities of the purified enzyme II responded similarly to temperature and pH, with optima at 70°C and pH 5.5–6.0. Both activities were activated by Ca 2+ and inhibited by Hg 2+ , Fe 3+ , NBS, DBS, SDS and urea to almost the same extent. Both activities were also inhibited competitively by CDs. Enzyme II catalyzed the hydrolysis of α‐1,6‐glucosidic linkages in maltosyl‐ and maltotriosyl‐α‐CD as well as that of α‐1,4‐bonds in amylose and related linear malto‐oligosaccarides larger than maltotriose, but exhibited no action on panose, isopanose or glucosyl α‐CD.