Phosphorylation of rat liver glycogen synthase by phosphorylase kinase.

Glycogen synthase was phosphorylated in vivo by perfusing rat liver or incubating liver cells with [32P]phosphate. It was then isolated by immunoprecipitation and subjected to exhaustive tryptic proteolysis. The trypsin-derived [32P]phosphopeptides were separated by high pressure liquid chromatography (HPLC). Incubation of in vivo phosphorylated synthase with endogenous synthase phosphatase to convert synthase D to synthase R resulted in removal of phosphate from all of the labeled phosphopeptides. In prelabeled liver cells treated with glucagon or glucose, the activities of synthase and phosphorylase changed in the direction expected. The total labeling in the immunoprecipitated synthase was found to be increased to 126% and decreased to 67% of the control with glucagon and glucose treatment, respectively. When the HPLC [32P]phosphopeptide profile of synthase from glucagon-treated animals was compared with that of controls, there were only minor differences in the two profiles. All the peaks were present and the proportion of labeling in each remained similar. There also was only a modest change in the [32P]phosphopeptide profile with glucose treatment when compared with that of controls. These results indicate that regulation of synthase activity in the hepatocyte involves changes in phosphorylation at multiple sites. Indeed, in 32P-labeled liver cells, all of the labeled sites appeared to be involved.Key words: glycogen synthase, liver, phosphorylation state, glucose treatment, glucagon treatment.

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Purification and phosphorylation of rat liver glycogen synthase.

Journal of Biological Chemistry ◽

10.1016/s0021-9258(18)50431-2 ◽

1979 ◽

Vol 254 (14) ◽

pp. 6739-6745 ◽

Cited By ~ 8

Author(s):

M F Jett ◽

T R Soderling

Keyword(s):

Rat Liver ◽

Glycogen Synthase ◽

Liver Glycogen

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Mechanisms underlying enhanced glycogenolysis in livers of 3,5,3'-triiodothyronine-treated rats

AJP Endocrinology and Metabolism ◽

10.1152/ajpendo.1990.258.1.e109 ◽

1990 ◽

Vol 258 (1) ◽

pp. E109-E116 ◽

Cited By ~ 1

Author(s):

S. Nebioglu ◽

P. Wathanaronchai ◽

D. Nebioglu ◽

E. L. Pruden ◽

D. M. Gibson

Keyword(s):

Glycogen Phosphorylase ◽

Glycogen Synthase ◽

Liver Glycogen ◽

Phosphorylase Kinase ◽

Feeding Schedule ◽

Glycogen Accumulation ◽

Meal Feeding ◽

Inducible Systems ◽

Alpha Glucosidase ◽

Experimental Group

Rats trained on a diurnal controlled meal-feeding schedule and injected with a single dose of 3,5,3'-triiodothyronine (T3) failed to accumulate liver glycogen and incorporated less D-[6-3H]glucose into glycogen than normally observed during the feeding period. In the experimental group, the concentration of liver adenosine 3',5'-cyclic monophosphate (cAMP) did not fall during feeding and the pattern of activities of glycogen phosphorylase, glycogen synthase, and phosphorylase kinase remained conductive to glycogenolysis. Liver lysosomal alpha-glucosidase activity normally fell during feeding periods. After T3 treatment the activities of alpha-glucosidase and two lysosomal cathepsins (B1 and D) were elevated. The evidence suggests that T3 may induce both liver phosphorylase kinase and lysosomal alpha-glucosidase. This outcome of T3 excess, in concert with previously described T3-inducible systems, provides a plausible explanation for the failure of glycogen accumulation in this experimental model.

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