Action Patterns of Phosphorylase and Glycogen Synthetase on Glycogen

Abstract

The action patterns of liver and muscle glycogen synthetases and of muscle phosphorylase b on glycogen samples of different molecular weight and on β‐amylase limit dextrins were studied. For this purpose a method for measuring the number of newly added glucose residues that are at non‐reducing ends was developed.It was found that glucose transfer to the non‐reducing ends of glycogen catalyzed by liver glycogen synthetase and muscle phosphorylase followed a Poisson distribution.The number of outer chains in the glycogen molecules available to both enzymes appeared to be smaller than the actual number of outer chains in the polysaccharide. The number of such available chains diminished as the glycogen was heavier. For the same glycogen sample, the number of available chains to phosphorylase appeared to be equal or smaller than that to glycogen synthetase.It was found that muscle phosphorylase transferred 1.2 to 1.4 glucose moieties successively per outer chain, independently of the molecular weight of the glycogen.The number of glucose units added successively to the non‐reducing ends of glycogen by liver glycogen synthetase increased from 1.7 to 6.8 with the molecular weight of the polysaccharide.Both phosphorylase and liver glycogen synthetase transferred more glucose units in a repetitive way to the same outer chain of the β‐amylase limit dextrin than to the same outer chain of the undegraded glycogen.Muscle glycogen synthetase transferred a greater number of glucose units successively per outer chain of glycogen than the liver enzyme.