Isolation of Protein-Glycogen Complexes from Rat Skeletal Muscle in Acute Uremia: Role of Serine

Abstract

Abstract

Attempts were made to isolate an intact protein–glycogen complex from rat skeletal muscle in acute and chronic uremia and after different treatment regimes. In control animals the amount of glycogen in the 30-pellet fraction was 16.5 mg and in rats with chronic uremia 27.6 mg. The yields of glycogen phosphorylase and synthetase do not correlate with the quantity of glycogen during isolation. In the presence of ATP, calcium, and magnesium, flash activation of phosphorylase was four to six times slower in rat than in rabbit muscle. In acute uremia, after feeding a mixed low-protein diet and Walser ketoacid mixture, a protein–glycogen complex could not be isolated. Additional administration of propranolol resulted in yields of only 10 and 7 μg glycogen after binephrectomy and ureter ligation, respectively. In contrast, glycogen concentration increased dramatically after sham operation (4.55 mg glycogen/mg protein). Additional administration of high doses of serine resulted in an increase of glycogen in the complex of 21.5 mg (134.3 μg glycogen/mg protein) in acute uremia. Kinetic analysis of phosphorylase activation in the presence of ATP, calcium, and magnesium indicated an intact protein–glycogen complex under these conditions. Glycogen concentrations were correlated with phosphorylase phosphatase activity. Constant amounts of sarcoplasmic reticulum calcium ATPase were isolated under all conditions tested. Our data suggest a key role of serine in the glycogen metabolism of muscle in acute uremia.