Enzymes in a Glycogen Storage Myopathy.

McArdle has reported a "myopathy due to a defect in muscle glycogen breakdown"' which appears to be a type of glycogen storage disease distinct from the previously reported classes.2 Schmid and Mahler' using muscle homogenates from a patient similar to the one described by McArdle have found that lactate is formed from added glucose 1-phosphate at a rate comparable to that of controls, but addition of muscle glycogen did not increase production of lactate. The content of glycogen in the muscles of this patient ranged from 2.4 to 3.0 per cent. Estimation of phosphorylase indicated a markedly reduced activity of this enzyme. Recently it has become apparent4-8 that there is a uridine linked pathway of glycogen synthesis present in animal tissues which involves two enzymes UDPGt pyrophosphorylase, and UDPG glycogen transglucosylase. It was therefore of interest to determine the enzymes of the uridine linked pathway in the muscle of a patient with McArdle's disease. Schmid, Robbins, Traut, and Lipmann9 have already estimated levels of phosphorylase, phosphoglucomutase, and UDPG glycogen transglucosylase. We report here further results with a sample of the same muscle biopsy, including confirmation of the extremely low phosphorylase activity, and in addition normal activities of UDPG pyrophosphorylase, amylo1,6-glucosidase, and phosphoglucomutase. Materials and Methods.The biopsy of the patient with the disease was obtained from the back. Two control biopsies of rectus and pectoral muscles were obtained during surgical procedures.: Homogenates of the rapidly frozen tissue (1:10 w/v) were made in 0.05 M Tris 0.005 M EDTA pH 8. Amylo-1,6-glucosidase was determined by the method of Hers (10), using phosphorylase limit dextrin instead of glycogen. UDPG pyrophosphorylase, phosphoglucomutase, and phosphorylase were determined spectrophotometrically (see Table I), using extracts prepared from homogenates by centrifugation at 3000 X g for 10 minutes. Activities have been expressed in the units used by Hers.'0 Results and Comments. A phosphorylase activity corresponding to 0.23 per cent of the control value was found in the diseased muscle (Table 1). No significant differences in the activities of amylo-1,6-glucosidase, phosphoglucomutase, or UDPG pyrophosphorylase were noted when compared to controls. It appears that the increased muscle glycogen content in this disease is associated with a markedly diminished phosphorylase activity. From the present and previous data9 it is apparent-that the two enzymes of the uridine pathway are present in the diseased muscle. There appears to be no deficiency in phosphoglucomutase or amylo-1,6-glucosidase activities. Previous experiments have shown that activation of phosphorylase by epinephrine or glucagon is associated with glycogen breakdown. "I Glycogen synthesis stimulated by insulin in rat diaphragm in short time experiments takes place with a ratio of inorganic phosphate to glucose 1-phosphate of 305.7 Activation of phosphor~ylase in muscle homogenates by addition of phosphorylase kinase results in