Crystallization and properties of human muscle phosphorylases a and b.

Much attention has been centered recently on the pathways of glycogen metabolism. The demonstration of the presence of a uridine diphosphoglucose-linked pathway for glycogen synthesis (1) and the extensive studies which followed (Z-6) have provided strong evidence for the existence in muscle of a metabolic cycle in which the uridine pathway is involved in the synthesis and phosphorylase catalyzes the degradation of glycogen. Particular support for this formulation came from the discovery of a human myopathy (7, 8) in which muscle biopsy revealed a high glycogen content accompanied by very low phosphorylase levels but a normal uridine diphosphosphoglucose-enzyme system. The existence of a disease in man involving a deficiency of phosphorylase as well as the usefulness of having the pure human enzyme for comparative biochemical studies prompted the present work. This paper deals with the purification of phosphorylase b from human autopsy skeletal muscle by ammonium sulfate,fractionation and column chromatography on anion exchange cellulose. As with rabbit muscle phosphorylase b (9, lo), crystallization of the human enzyme is achieved in the presence of Mg++ ions and adenylic acid. The human phosphorylase b can be converted to phosphorylase a with purified rabbit phosphorylase kinase (11) and this form of the enzyme also crystallizes readily. Properties of both enzymes, including sedimentation constants, pH optima, pyridoxal phosphate content, and immunochemical specificity, are also described. A preliminary report of this work has been previously presented (12).