Studies on carbohydrate-metabolizing enzymes. 3. Yeast branching enzyme.

enzymes on oX-D-glucosyl phosphate also yields a branched polysaccharide, although Q-enzyme alone has no action on the glucoside. In the animal kingdom a related enzyme system may be partly responsible for glycogen synthesis. Muscle phosphorylase synthesizes amylose-type chains from OC-D-glucosyl phosphate and the concurrent action of this enzyme and an enzyme preparation (branching factor or supplementary enzyme) from heart or liver extracts gave a glycogen-type polysaccharide, since the latter gave a red-brown coloration with iodine and, unlike amylose, could function as a primer for muscle phosphorylase (Cori & Cori, 1943). In general, however, the branching enzymes from animal tissues have not been highly purified and the products of enzyme action have not been rigidly characterized. Glycogen is one of the reserve polysaccharides of brewer's yeast (Manners & Khin Maung, 1955a); hence, extracts of this yeast should provide a source of branching enzyme. This enzyme was first encountered as an impurity in yeast-phosphorylase preparations (unpublished work), which, acting on -L-D-glucosyl phosphate, synthesized a branched polysaccharide which had a fi-amylolysis limit of 44% and gave a red-brown stain with iodine. This paper describes some of the properties of partly purified yeast branching enzyme and its action on amylose. Furthermore, since yeast glycogen contains 7-8% of 1:6-glucosidic linkages, it was of interest to examine the action of yeast branching enzyme on an amylopectin containing only 4-5% ofbranch points. Preliminary accounts of some of this work have been published (Manners & Khin Maung, 1956; Gunja & Manners, 1959).