Comparison of two glucoamylases produced by Aspergillus oryzae in solid-state culture (Koji) and in submerged culture

Two extracellular glucoamylases (EC 3.2.1.3) of Aspergillus oryzae were purified from solid-state culture (S-GA) and from submerged culture (L-GA). The two glucoamylases have different molecular masses, 65 kDa for L-GA; 63-99 kDa for S-GA, and different isoelectric points, 4.2 for L-GA; 3.9 for S-GA. Almost all of the enzymatic characteristics of the two glucoamylases were similar, except for thermal stability, initial reaction velocity on pullulan and K-m value with soluble starch. Although L-GA could digest raw starch, S-GA demonstrated little activity with raw starch. Peptide mapping and amino acid composition showed that L-GA must be encoded by the glaA gene previously cloned as the glucoamylase-encoding gene from A. oryzae, bat S-GA had a different primary structure than the deduced glaA product. introduction of multiple copies of the glaA gene to A. oryzae caused on elevation of glucoamylase productivity of transformant in submerged culture but not in solid-state culture. These results suggested that the two forms of glucoamylases arise from different genes rather than result from proteolytic processing after polypeptide synthesis of a single protein.