The action of an amyloglucosidase of Aspergillus niger on starch and malto-oligosaccharides.

Earlier reports from a number of laboratories (l-3) have shown that Aspergillus niger produces several enzymes with ability to hydrolyze the a-~-(1 ---f 4) glucosidic linkages in starch and maltooligosaccharides. Important members of this group include a-amylase, amyloglucosidase and maltase. Within recent years there has been considerable interest in the amyloglucosidase group of enzymes since they are capable of converting starch completely to glucose (4-7). Evidence in the literature (1, 4) indicates that the enzymes of this group effect a hydrolysis of starch by a single chain mechanism in which glucose units are removed from the nonreducing end of a linear chain until complete hydrolysis of the chain has been effected. Although high yields of glucose are obtained from starch and amylopectin, reports on the ability of the enzyme to hydrolyze the a-~-(1 ---f 6) linkages in the branched polysaccharides are conflicting (4, 6). Little attention has been given to the elucidation of the action pattern of amyloglucosidase on malto-oligosaccharides or to the possibility of transglucosylic reactions (8) occurring during amyloglucosidase action. In our laboratories an amyloglucosidase of Aspergillus niger has been obtained in a highly purified state by a chromatographic procedure with the use of cellulose ion exchange materials. This enzyme has been used in studies reported herein on the mode of action of a representative amyloglucosidase on starch and on malto-oligosaccharides. The amyloglucosidase converted starch, amylose, amylopectin and amylodextrin to glucose in yields approximating complete conversion. Results of experiments in which malto-oligosaccharides labeled in position 1 with Cl4 were used as substrates for the enzyme, showed that the hydrolysis of these oligosaccharides begins at the nonreducing end of the molecules and continues by a multi-chain mechanism. The purified amyloglucosidase is capable of hydrolyzing maltose but is devoid of transglucosylic activity.