Biological actions of insulin are differentially regulated by glucose and insulin in primary cultured adipocytes. Chronic ability to increase glycogen synthase activity

To examine whether changes in the glycogen synthase protein concentration contribute to impaired insulin-stimulated glycogen metabolism in patients with noninsulin-dependent diabetes mellitus (NIDDM), muscle biopsies were taken before and after a 4-h euglycemic hyperinsulinemic clamp to measure glycogen synthase activity and glycogen synthase protein concentrations in 14 patients with NIDDM and in 17 control subjects. Nonoxidative glucose metabolism was reduced by 64% in patients with NIDDM compared with control subjects and correlated with insulin-stimulated glycogen synthase activity (r = 0.55, P < 0.05). The concentration of glycogen synthase protein in skeletal muscle was higher in patients with NIDDM than in control subjects (6.75 +/- 0.88 vs. 4.41 +/- 0.50 counts.min-1.micrograms protein-1, P < 0.05), whereas there was no significant difference in glycogen synthase mRNA concentration between the two groups. The glycogen synthase protein concentration correlated inversely with the rate of nonoxidative glucose metabolism (r = -0.63, P < 0.05). These findings indicate that the amount of glycogen synthase protein is increased in skeletal muscle of patients with NIDDM. The increase in the glycogen synthase protein may serve to compensate for a functional defect in the activation of the enzyme by insulin.

Download Full-text

Fasting and diabetes alter adipose tissue glycogen synthase

AJP Endocrinology and Metabolism ◽

10.1152/ajpendo.1984.247.5.e581 ◽

1984 ◽

Vol 247 (5) ◽

pp. E581-E584

Author(s):

H. R. Kaslow ◽

R. D. Eichner

Keyword(s):

Skeletal Muscle ◽

Adipose Tissue ◽

Enzyme Purification ◽

Glycogen Synthase ◽

Streptozotocin Diabetes ◽

Positive Cooperativity ◽

Maximal Activation ◽

Glucose Incorporation ◽

Glycogen Synthase Activity

In a previous report (J. Biol. Chem. 254: 4678-4683, 1979), we showed that fasting blunted the ability of insulin to promote glucose incorporation into glycogen in vitro. In addition, we showed that glycogen synthase activity was altered in two ways: the concentration of glucose 6-P causing half-maximal activation increased, and positive cooperativity appeared in the glucose 6-P activation of the enzyme. We now show that streptozotocin-diabetes causes the same changes in glucose incorporation and glycogen synthase activity. We show that these changes in glycogen synthase activity persist during enzyme purification; thus it is likely the changes are a result of a structural alteration of the enzyme. Because glycogenolysis of a glycogen particle from rabbit skeletal muscle also caused the appearance of positive cooperativity, we propose that both phosphorylation and glycogenolysis are involved in the appearance of positive cooperativity.

Download Full-text

Hyperglycemia reduces nitric oxide synthase and glycogen synthase activity in endothelial cells

Nitric Oxide ◽

10.1016/s1089-8603(02)00106-4 ◽

2002 ◽

Vol 7 (3) ◽

pp. 187-193 ◽

Cited By ~ 36

Author(s):

I Noyman ◽

M Marikovsky ◽

S Sasson ◽

A.H Stark ◽

K Bernath ◽

...

Keyword(s):

Nitric Oxide ◽

Endothelial Cells ◽

Nitric Oxide Synthase ◽

Glycogen Synthase ◽

Oxide Synthase ◽

Glycogen Synthase Activity

Download Full-text

Role of nuclear glycogen synthase and cytoplasmic UDP glucose pyrophosphorylase in the biosynthesis of nuclear glycogen in HD33 Ehrlich-Lettré ascites tumor cells.

The Journal of Cell Biology ◽

10.1083/jcb.89.3.475 ◽

1981 ◽

Vol 89 (3) ◽

pp. 475-484 ◽

Cited By ~ 18

Author(s):

C Granzow ◽

M Kopun ◽

H P Zimmermann

Keyword(s):

Tumor Cells ◽

Glycogen Synthase ◽

Glycogen Synthesis ◽

Membrane System ◽

Ascites Tumor ◽

Cell Nuclei ◽

Electron Microscopic ◽

Intact Cells ◽

Isolated Nuclei ◽

Glycogen Synthase Activity

Biochemical and autoradiographic evidence show both glycogen synthesis and the presence of glycogen synthase (UDP glucose [UDPG]: glycogen 4-alpha-D-glucosyltransferase; EC 2.4.1.11) in isolated nuclei of Ehrlich-Lettré mouse ascites tumor cells of the mutant subline HD33. 5 d after tumor transplantation, glycogen (average 5-7 pg/cell) is stored mainly in the cell nuclei. The activity of glycogen synthase in isolated nuclei is 14.5 mU/mg protein. At least half of the total cellular glycogen synthase activity is present in the nuclei. The nuclear glycogen synthase activity exists almost exclusively in its b form. The Km value for (a + b) glycogen synthase is 1 x 10(-3) M UDPG, the activation constant is 5 x 10(-3) M glucose-6-phosphate (Glc-6-P). Light and electron microscopic autoradiographs of isolated nuclei incubated with UDP-[1-3H]glucose show the highest activity of glycogen synthesis not only in the periphery of glycogen deposits but also in interchromatin regions unrelated to detectable glycogen particles. Together with earlier findings on nuclear glycogen synthesis in intact HD33 ascites tumor cells (Zimmermann, H.-P., V. Granzow, and C. Granzow. 1976. J. Ultrastruct. Res. 54:115-123), the results of tests on isolated nuclei suggest a predominantly appositional mode of nuclear glycogen deposition, without participation of the nuclear membrane system. In intact cells, synthesis of UDPG for nuclear glycogen synthesis depends on the activity of the exclusively cytoplasmic UDPG pyrophosphorylase (UTP: alpha-D-glucose-1-phosphate uridylyltransferase; EC 2.7.7.9). However, we conclude that glycogen synthesis is not exclusively a cytoplasmic function and that the mammalian cell nucleus is capable of synthesizing glycogen.

Download Full-text