Structural and Catalytic Properties of Lobster Muscle Glycogen Phosphorylase

Purification of lobster phosphorylase was achieved by a mild method which involves ammonium sulfate and diethylaminoethyl cellulose column chromatography. Both lobster phosphorylase b and a were crystallized by dialysis against 0.01 m EDTA, pH 6.8, which was 30% saturated in ammonium sulfate. Structural and catalytic studies on crystalline lobster phosphorylase are reported. Striking differences from rabbit muscle phosphorylase were found in the amino acid composition, association-dissociation behavior, catalytic efficiency at cold temperature, cold inactivation, energy of activation, and kinetic constants including the allosteric constant. The molecular weight and the extinction coefficient for lobster phosphorylase b are also reported in this study and a model is presented to account for the allosteric properties of this enzyme.