Isolation and characterization of glycogen branching enzyme from rabbit liver

Abstract

Glycogen branching enzyme was isolated from rabbit liver. The highly purified enzyme shows a monomer MW of 71,000 by sodium dodecyl sulfate-polyacrylamide gel electrophoresis and apparent MW of 93,000 by sucrose density gradient sedimentation and 52,000 by gel-exclusion chromatography on Sephacryl S-300. No glucosamine, mannosamine, galactosamine or sialic acid was detected in the protein. An amino acid analysis is reported. The spectrum of branching enzyme is that of a simple polypeptide, with .**GRAPHIC**. = 24.6. Highly purified branching enzyme consists of several closely related active enzyme forms that can be resolved by isoelectric focusing in polyacrylamide gel. The major species of pI [isoelectric point] 5.7 is flanked by less abundant forms of pI 5.6 and 5.8. Seemingly identical enzyme forms are observed in crude extracts of rabbit liver, skeletal muscle, brain and heart, although the absolute and relative concentrations vary among the tissues. Branching enzyme apparently does not exhibit tissue-specific isoenzymes.