Biochemical characterization of glucoamylase from the hyperproducer exo-1 mutant strain of Neurospora erassa

Abstract

The Neurospora crassa exo-1 mutant produced maximum extracellular glucoamylase activity in media supplemented with starch as the sole carbon source. The apparent molecular mass of the enzyme was 82 kDa (SDS-PAGE and gel filtration). The enzyme was a glycoprotein with 5.1 % carbohydrate content and exhibited a temperature optimum of 60 °C. The pH optima were 5.4 and 5.0 for glucoamylase and maltase activities, respectively. Cu 2+ inhibited maltase activity while Mn 2+ stimulated glucoamylase activity. The purified enzyme hydrolyzed branched substrates more efficiently than linear substrates. Starch was the best substrate utilized and amylose was hydrolyzed faster than maltose. Kinetic experiments suggested that maltose and starch were hydrolyzed at the same catalytic site.