Comparative Studies on Glycogen Phosphorylase

The isolation and crystallization of both forms of glycogen phosphorylase from human skeletal muscle (1) have made possible a detailed study of the properties of these enzymes in comparison with those of rabbit skeletal muscle (2, 3). Phosphorylase b and a from both species have been shown to crystallize under similar conditions and to have similar pH optima, electrophoretic mobilities, sedimentation constants, and pyridoxal 5’phosphate content (1). Phosphorylase b from human muscle, like phosphorylase b from rabbit muscle, can be converted to phosphorylase a by a purified preparation of phosphorylase 6 kinase isolated from rabbit muscle. The reaction requires Mg++ and adenosine triphosphate and is accompanied by the incorporation of 4 moles of phosphate per mole of phosphorylase u.l Recently it has been shown that rabbit and human muscle phosphorylases could be distinguished immunologically when injected into the goat (4). A previous study (1) indicated that no differences could be found when rooster antibodies to phosphorylase b were used. Since the structure of the specific site phosphorylated during the conversion of rabbit muscle phosphorylase b to a had previously been determined (5), it was of some interest to investigate the structure of the corresponding site of the human enzyme in order to determine the importance of this region of the two proteins in the immunological response. A preliminary account of the work has been presented (6).