The Purification and Properties of Rabbit Skeletal Muscle Glycogen Synthase

Abstract

Glycogen synthase a was purified over 500-fold by a procedure which involved solubilisation of the enzyme from a protein-glycogen complex by the action of endogenous phosphorylase and debranching enzyme, followed by DEAE-cellulose chromatography, and either gel filtration on Sepharose 4B or fractionation with polyethylene glycol. 15 mg of protein could be obtained from 1000 g of muscle in five days, corresponding to a yield of 20%. The purity was over 90% as judged by gel electrophoresis and ultracentrifugal analysis. The amino acid composition was determined and the absorption coefficient, A1%280 NM, measured refractiometrically was 13.4. Glycogen synthase a sedimented as two major components, both of which were enzymatically active. The smaller species (13.3 S) comprised 85% and the larger species (19.OS) 15% of the material. The molecular weight of the 13.3-S component was determined to be 377000 by high-speed sedimentation equilibrium centrifugation. The subunit molecular weight measured by gel electrophoresis in the presence of sodium dodecylsulphate was 88 000 indicating that the 13.3-S species is a tetramer. The properties of the enzyme are compared to those obtained by other workers.