Amylases of the thermophilic fungus Thermomyces lanuginosus: Their purification, properties, action on starch and response to heat

A thermophilic fungus Thermomyces lanuginosus, strain IISc 91, secreted one form each of alpha-amylase and glucoamylase during growth. Both enzymes were purified to homogeneity by ion-exchange and gel-filtration chromatography and obtained in mg quantities. alpha-Amylase was considered to be a dimeric protein of similar to 42 kDa and contained 5% (by mass) carbohydrate. It was maximally active at pH 5.6 and at 65 degrees C. It had an activation energy of 44 kJ mol(-1). The apparent K-m for soluble starch was 2.5 mg ml(-1). The enzyme produced exceptionally high levels of maltose from ram potato starch. At 50 degrees C, the enzyme mas stable for > 7 h. At 65 degrees C, alpha-amylase was nearly 8-times more stable in the presence of calcium. Addition of calcium increaed the melting temperature of alpha-amylase from 66 degrees C to 73 degrees C. Upon incubation at 94 degrees C, alpha-amylase mas progressively and irreversibly inactivated, and converted into an inactive 72 kDa trimeric species. Glucoamylase was a monomeric glycoprotein of similar to 45 kDa with a carbohydrate content of 11% (by mass). It effected up to 76% conversion of starch in 24 h producing glucose as the sole product. Its apparent K-m for soluble starch was 0.04 mg ml(-1) and V-max was 660 pmol glucose min(-1) mg protein(-1). It also hydrolyzed maltose. Its activity on maltooligosaccharides increased with the chain length of the substrates. Glucoamylase was stable at 60 degrees C for over 7 h. Its activation energy was 61 kJ mol(-1). Glucoamylase did not show synergistic effect with alpha-amylase. The properties of alpha-amylase and glucoamylase of Thermomyces lanuginosus strain IISc 91 suggest their usefulness in the commercial production of maltose and glucose syrups