Studies on the Carbohydrate-Binding Specificity of Glycogen Phosphorylases by Means of Affinity Electrophoresis

Dissociation constans of rabbit muscle glycogen phosphorylases for various carbohydrates were measured by affinity electrophoresis. 1. Dissociation constants for glycogen at 5℃ was about one five-hundredth of that at 42.5℃. In other words, affinity of phosphorylase for glycogen at 5℃ was approximately 500 times stronger than that at 42.5℃. 2. Thermodynamic constants (△H^。 and △S^。) were calculated from the van't Hoff plots. The results indicated that the interaction between phosphorylase and glycogen was an exothermic reaction and the enzyme became of more ordered conformation. 3. The size of the carbohydrate-binding site of phosphorylase corresponds to that of maltohexaose. Cyclic maltose-type oligosaccharides competed with glycogen for the carbohydrate-binding site of phosphorylase. 4. All of the results mentioned above were quite similar for both phosphorylases a and b. From these results, it is concluded that glycogen and maltose-type oligosaccharides bind to phosphorylase at the glycogen storage site, and this site exists independently of the catalytic site and the AMP-binding site.