1. Regulation of Rat Liver Glycogen Synthetase D
- Author
-
Michael J. Ernest and Ki-Han Kim
- Subjects
Glycogen binding ,biology ,Glycogen ,Chemistry ,Cell Biology ,Biochemistry ,Molecular biology ,Enzyme assay ,Glycogen debranching enzyme ,chemistry.chemical_compound ,Glycogen phosphorylase ,Glucose 6-phosphate ,Glycogen branching enzyme ,biology.protein ,Glycogen synthase ,Molecular Biology - Abstract
Reaction of four of the eight sulfhydryl groups per subunit of rat liver glycogen synthetase D through mixed disulfide formation with oxidized glutathione leads to inactivation of the enzyme and its dissociation from glycogen. The differential protection offered by glucose 6-phosphate against inactivation and dissociation permits determination of the number of sulfhydryl groups involved in each process. Modification of the first sulfhydryl group had no effect on enzyme activity or glycogen binding. Reaction of the second sulfhydryl group led to complete inactivation of the enzyme and was accompanied by an increase in the Ka for glucose-6-P. Modification of two more sulfhydryl groups per subunit resulted in release of the enzyme from glycogen. Gel filtration experiments revealed that disruption of the glycogen-glycogen synthetase D complex was a consequence of dissociation of the enzyme itself into a subunit (mol wt 86,000) which could not bind glycogen. The enzyme-glycogen complex could be reconstituted from glycogen and glycogen-free, inactive glycogen synthetase D by treatment with glucose-6-P. Reduction with dithiothreitol, which by itself failed to restore the complex, significantly lowered the concentration of glucose-6-P required to fully achieve reconstitution. Treatment with glucose-6-P, but not reduction with dithiothreitol, reassociated the inactive subunit into a high molecular weight species which is the form capable of binding glycogen. These results suggest that glucose-6-P plays an important role in maintaining the glycogen-glycogen synthetase D complex.
- Published
- 1974