Hormonal Control of Glycogen Metabolism

The plasma cortisol concentration and liver cytosolic glucocorticoid receptor activities of continuously swimming, food-deprived coho salmon (Oncorhynchus kisutch) did not differ from those of resting, fed fish. Plasma glucose concentration was significantly higher in the exercising, starved fish, but there were no significant differences in either hepatic glycogen concentration or hepatic activities of glycogen phosphorylase, glycogen synthase, pyruvate kinase, or lactate dehydrogenase between the two groups. Total glucose production by hepatocytes did not differ significantly between the two groups; glycogen breakdown accounted for all the glucose produced in the resting, fed fish whereas it explained only 59% of the glucose production in the exercised animals. Epinephrine and glucagon stimulation of glucose production by hepatocytes was decreased in the exercised fish without significantly affecting hepatocyte glycogen breakdown in either group. Insulin prevented glycogen breakdown and enhanced glycogen deposition in exercised fish. The results indicate that food-deprived, continuously swimming coho salmon conserve glycogen by decreasing the responsiveness of hepatocytes to catabolic hormones and by increasing the responsiveness to insulin (anabolic hormone).

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The Hormonal Control of Glycogen Metabolism. Phosphorylation of Protein Phosphatase Inhibitor-1 in vivo in Response to Adrenaline

European Journal of Biochemistry ◽

10.1111/j.1432-1033.1979.tb13109.x ◽

1979 ◽

Vol 97 (1) ◽

pp. 251-256 ◽

Cited By ~ 110

Author(s):

J. Gordon FOULKES ◽

Philip COHEN

Keyword(s):

Protein Phosphatase ◽

Glycogen Metabolism ◽

Hormonal Control ◽

Phosphatase Inhibitor ◽

Protein Phosphatase Inhibitor

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Mutations of the serine phosphorylated in the protein phosphatase-1-binding motif in the skeletal muscle glycogen-targeting subunit

Biochemical Journal ◽

10.1042/bj3460077 ◽

2000 ◽

Vol 346 (1) ◽

pp. 77-82 ◽

Cited By ~ 9

Author(s):

Jun LIU ◽

Jun WU ◽

Carey OLIVER ◽

Shirish SHENOLIKAR ◽

David L. BRAUTIGAN

Keyword(s):

Skeletal Muscle ◽

Muscle Glycogen ◽

Protein Phosphatase ◽

Glycogen Metabolism ◽

Binding Activity ◽

Hormonal Control ◽

Protein Phosphatase 1 ◽

Binding Motif ◽

Unique Contribution ◽

Skeletal Muscle Glycogen

Cellular functions of protein phosphatase-1 (PP1) are determined by regulatory subunits that contain the consensus PP1-binding motif, RVXF. This motif was first identified as the site of phosphorylation by cAMP-dependent protein kinase (PKA) in a skeletal muscle glycogen-targeting subunit (GM). We reported previously that a recombinant fusion protein of glutathione S-transferase (GST) and the N-terminal domain of GM [GST-GM-(1-240)] bound PP1 in a pull down assay, and phosphorylation by PKA prevented PP1 binding. Here we report that substitution of either Ala or Val for Ser-67 in the RVS67F motif in GST-GM-(1-240) essentially eliminated PP1 binding. This was unexpected because other glycogen-targeting subunits have a Val residue at the position corresponding to Ser-67. In contrast, a mutation of Ser-67 to Thr (S67T) in GST-GM(1-240) gave a protein that bound PP1 the same as wild type and was unaffected by PKA phosphorylation. Full length GM tagged with the epitope sequence DYKDDDDK (FLAG) expressed in COS7 cells bound PP1 that was recovered by co-immunoprecipitation, but this association was prevented by treatment of the cells with forskolin. By comparison, PP1 binding with FLAG-GM(S67T) was not disrupted by forskolin treatment. Neither FLAG-GM(S67A) nor FLAG-GM(S67V) formed stable complexes with PP1 in COS7 cells. These results emphasise the unique contribution of Ser-67 in PP1 binding to GM. The constitutive PP1-binding activity shown by GM(S67T) opens the way for studying the role of GM multisite phosphorylation in hormonal control of glycogen metabolism.

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