PHYSICAL AND CHEMICAL STUDIES ON CRYSTALLINE RABBIT MUSCLE PHOSPHOGLUCOMUTASE . MULTIPLE FORMS

Crystalline preparations of rabbit muscle phosphoglucomutase have been resolved into four fractions using the technique of isoelectric focusing. The fractions contained 82,8,6, and 4%, respectively, of the original enzyme and each was enzymatically active and recovered in the phosphorylated form. Similar fractionation was demonstrated using acrylamide gel electrophoresis. Physical and chemical studies on the parent crystals indicated that the phosphoglucomutase “isozymes” were not due to molecular aggregation or subunit rearrangement. The molecular weight of crystalline rabbit muscle phosphoglucomutase by sedimentation equilibrium was found to be 64,900. Sedimentation equilibrium analyses of reduced and carboxymethylated phosphoglucomutase in the presence of 5 M guanidine hydrochloride gave a molecular weight of 64,000, indicating that there are no subunit structures in rabbit muscle phosphoglucomutase. The J20,W value, calculated from sedimentation velocity data, was 3.82 S. Calculation of the partial specific volume from amino acid composition data gives a value of 0.737. The isoelectric pH of phosphoglucomutase, using the techniques of isoelectric focusing, was found to be 6.80. © 1969, American Chemical Society. All rights reserved.