Specific Inhibition by Cyclodextrins of Raw Starch Digestion by Fungal Glucoamylase

Abstract

α-, β-, and γ-cyclodextrins (CDs) completely inhibited raw starch digestion by glucoamylase I (GA I, MW 90, 000) from Aspergillus awamori var. kawachi, and inhibited by 85% the raw starch adsorption of GA I at the CD concentrations of 1-5 ImM. CDs at 1-5 mM did not inhibit gelatinized starch hydrolysis by GA I, but at the concentration of 50 mM, they inhibited such hydrolysis slightly. GA I was specifically adsorbed onto CD-Sepharose 6B, but glucoamylase I' (GA I', MW 73, 000), which does not adsorb onto or digest raw starch, from the same strain was not adsorbed onto that gel. The adsorption of the glucoamylases onto raw starch and CD-Sepharose 6B was correlated to their digestion of raw starch. The hydrophobic adsorption of GA I onto CDs and raw starch occurred competitively at the Cp region, which is on the C-terminal side of Gp-I in the site for raw starch affinity of GA I, and inclusion complexes were formed.