Isolation and Comparison of Phosphorylase b Isozymes in Pig Heart

Abstract

Three phosphorylase [EC 2.4.1.1] b isozymes were found in pig heart and isolated by chromatography on a starch column. These enzymes were designated as enzymes I, II and III in the order of elution from the column. Several of their molecular and catalytic properties were compared, and they were also compared with those of skeletal muscle enzyme. 1. A procedure for enzyme purification on a starch column was described. 2. On ultracentrifugation, all phosphorylases showed sedimentation coefficients of about 8.5S. 3. On electrophoresis, enzyme I migrated the fastest toward the anode at pH 8.5, II at an intermediate rate and III the slowest. Recombination of isozyme molecules was studied. 4. The effects of treatment with urea, heat and low temperature on the activities were examined. 5. The Michaelis constants for G1P and AMP were measured. 6. The effects of G6P and ATP on the activities were studied. G6P only inhibited enzyme I. 7. The properties of enzyme III were the same as those of skeletal muscle enzyme.