The Hyperdigestion of Raw Starch by a Carbohydrate-Rich Glucoamylase from a Protease- and Glycosidase-Negative Mutant ofAspergillus awamorivar.kawachiF-2035

Abstract

A protease- and glycosidase-negative mutant F-2035, of Aspergillus awamori var. kawachi has been isolated that produces a glucoamylase that contains a large carbohydrate moiety and has enhanced ability to digest raw starch (GA MU-H; MW, 110,000). This enzyme digested raw corn starch 2.5 times faster than did the parental glucoamylase I (GA I; MW, 90,000). When grown from an enriched seed culture, this mutant also produced a glucoamylase with less ability to digests raw starch (GA MU-L; MW, 110,000). Its activity was 25% of that of GA MU-H with raw starch. Both GA MU-H and GA MU-L proved to be identical to GA I in terms of adsorption to raw starch, molar activity against gelatinized starch, amino acid composition, and terminal amino acid sequence. The carbohydrate contents of GA I, GA MU-H, and GA MU-L were 17%, 33%, and 33% by weight, respectively. The carbohydrates of GA I and GA MU-H were mostly mannose, but that of GA MU-L was composed of mannose (71%) and glucose (26%). Partial removal of the carbohyd...