糸状菌グルコアミラーゼの構造と機能に関する研究

抄録

(1) One form and three forms (GI, GII, and GIII) of glucoamylases were purified from crude commercial preparation of Aspergillus niger and Rhizopus delemar, respectively, to be homogenous on disc- and SDS-gel electrophoresis and free from a-amylase and phosphatase. Neither purified glucoamylase from A. niger nor R. delemar could completely hydrolyze various kinds of starches because of the presence of phosphate esters attached to C-3 or C-6 of glucosyl residue, and left a limit-dextrin of large-molecular weight. The concomitant actions of a-amylase and phosphatase with the glucoamylases were found to be necessary for complete hydrolysis of these starches. (2) R. delemar GIII was suggested to have a specific affinity site, "starch-binding site, " for high-molecular-weight substrates from the results of kinetic study and modification with chymotrypsin. GI and GII were suggested to be derived from GIII by the post-secretional modification. (3) Aspergillus sp. K-27 produced the enzyme (s) which degraded well the raw starches. Glucoamylase and a-amylase were separated and purified from the culture filtrate of the fungus. The former seemed to have the "starch-binding site, " based on the results of partial proteolysis and kinetic studies. The latter showed low activity on raw starches but synergistically enhanced the degradation of starch granules with glucoamylase. The removal of the starch-binding site from glucoamylase reduced the ability of raw-starch degradation and abolished the synergistic effect with a-amylase. These results suggested that the starch-binding site plays an importantrole in raw-starch hydrolysis.