Action of glucoamylase from Aspergillus niger on phosphorylated substrate

Glucoamylase (1,4-alpha-D-glucan glucohydrolase, EC 3.2.1.3) from Aspergillus niger was purified to be free from alpha-amylase and phosphatase (glucose 6-phosphate as substrate). The phosphatase was well separated from the glucoamylase by phosphocellulose ion-exchange chromatography. The glucoamylase action was prevented by the esterified phosphate groups of the substrate. Thus, the extensive action of the glucoamylase on potato starch exposed the 6-posphorylglucosyl residue of the starch at the non-reducing terminal and large molecular weight limit dextrins remained. The concomitant action of the phosphatase was necessary for the complete degradation of the starch.