Glucoamylase activity from the thermophilic fungus Scytalidium thermophilum. Biochemical and regulatory properties

A glucoamylase activity produced by the thermophilic fungus Scytalidium the rmophilum was purified 6.8-fold by ion exchange chromatography. The protein exhibited a molecular mass of about 86 kDa (7% PAGE and SDS-PAGE), or 68.5 kDa (Bio Sil SEC-400 FPLC). The pi of the enzyme was 8.4. Optima of pH and temperature, with starch or maltose as substrates were, 6.5/60 degrees C a nd 5.0/55 degrees C, respectively. The enzyme had a half-life of 22 min at 55 degrees C with starch as substrate, and it was fully stable with maltose . Maltase activity was activated by 10 mM Ba++ (7.8%); Mn++ (12.4%) or Mg+ (28%). The enzyme contained approximately 25.5% carbohydrate. K-m and V-ma x values for starch and maltose were 0.28 mg/ml, 67.2 U/mg protein and 1.40 mg/ml, 5.61 U/mg protein, respectively. The products of hydrolysis of star ch, detected by thin layer chromatography, showed only glucose after 30 min , indicating a glucoamylase activity. The amino terminal sequence of the pu rified protein showed 93% homology with a glucoamylase activity purified fr om Humicola grisea var, thermoidea.