Purification and characterization of extracellular glucoamylase from the thermophilic Thermomyces lanuginosus

A thermostable extracellular glucoamylase from Thermomyces lanuginosus in static culture was purified to SDS-PAGE homogeneity by fractional ammonium sulphate precipitation, ion-exchange chromatography on DEAE-Toyopearl, Butyl-Toyopearl hydrophobic interaction chromatography, gel filtration on Sephacryl S-300 and ion-exchange chromatography on FPLC MonoQ. The molecular weight of the enzyme, consisting of a single polypeptide, was estimated to be 72 000 by SDS-PAGE. The glucoamylase exhibited maximal activities at pH 5.0. The optimum temperature for the activity was 70 degrees C. The enzyme was thermostable at 60 degrees with half-lives at 70 degrees of 20 min and 80 degrees of about 6 min. The glucoamylase was a glycoprotein with 11.4% carbohydrate content. The enzyme hydrolysed soluble starch, amylose, amylopectin, dextrin, glycogen, maltotroise and maltose. Starch was the best substrate.