Studies on carbohydrate-metabolizing enzymes. 7. Yeast isoamylase

Abstract

Extracts of brewer''s yeast contain a debranching enzyme, isoamylase, which may be isolated by acetone fractionation at[long dash]7[degree]. Enzyme action on glycogen is optimum at about pH 6 and 25[degree], is inhibited by borate (10 m[image]) and mercuric chloride (0 .1 m[image]) but not by sulfhydryl reactants. The reaction is characterized by a marked increase in iodine-staining power and [beta]-amylolysis limit but [alpha]-(1[long dash]4)-glucosidic linkages in glycogen are not attacked. Enzyme action is incomplete, only the outer [alpha]-(1 [forward arrow] 6)-glucosidic linkages being hydrolysed. Isoamylase differs from the plant and animal debranching enzymes [R-enzyme and amylo-(l [forward arrow] 6)-glucosidase] since both amylo-pectin and glycogen are substrates. Purified isoamylase has no action on maltose, isomaltose or maltotriose. Isoamylase is also present in baker''s yeast.