Glucoamylase from the Predacious Fungus Arthrobotrys conoides: a Cationic Enzyme with High Debranching Activity and Raw Starch Digestibility

The extracellular amylolytic activity elaborated by the nematophagous fungus Arthrobotrys conoides was found to resolve into 2 amylolytic peaks when fractionated on Sephadex G-100 column. Around 80% of the eluted glucoamylase activity was attributed to peak I (GA A). GA A being cationic in nature was purified about 70-fold with 57% yield by negative chromatography on DEAE Sephadex at pH 7.0. The enzyme was stable over a broad pH range of 4.8–9.0. K_M for the linear polysaccharide amylose was 0.34 mg/mL. Enzyme showed high affinity for the branched polysaccharides as the K_M values for amylopectin, glycogen and starch were 0.056, 0.062 and 0.065 mg/mL, respectively. The enzyme clearly demonstrated raw starch digestibility. Probable involvement of Trp and His residues in enzyme catalysis was elucidated using group-specific reagents.