Purification and some properties of an alpha-amylase glucoamylase fusion protein from Saccharomyces cerevisiae

A fusion gene containing the Bacillus subtilis alpha -amylase gene and Aspergillus awamori glucoamylase cDNA was expressed in Saccharomyces cerevisiae. The resulting bifunctional fusion protein having both alpha -amylase and glucoamylase activities secreted into the culture medium was purified to apparent homogeneity by affinity chromatography and gel filtration on Sephadex G-100. The enzyme had an apparent molecular mass of 150 kDa and showed an optimum pH and temperature of 6.0 and 60 degree C, respectively. The main hydrolysis products from soluble starch were glucose and maltose.