A study of the mechanism of action of phosphorylase B using isotope-labelled substrates

We have measured the alpha-deuterium and alpha-tritium secondary kinetic isotope effects on the synthesis and phosphorolysis of glycogen catalyzed by glycogen phosphorylase B (EC 2.4.1.1). The isotope-labeled substrates glucose-1T-1-phosphate and 1C14-glucose-1D-1-phosphate were used in the experiments, together with 6T-glucose-1-phosphate and C14-glucose-1-phosphate as controls. Measurement by the double label technique showed that both effects studied were equal to zero within the limits of experimental error. The possible mechanism of action of phosphorylase B is discussed.