Related Experiment Videos
Interconversion between multiple glucose 6-phosphate-dependent forms of glycogen synthase in intact adipose tissue
The Journal of Biological Chemistry
|June 10, 1979
Summary
Hormones regulate glycogen synthesis in adipose tissue by interconverting glucose-6-phosphate-dependent forms of glycogen synthase. This interconversion, measured by the activation constant (A0.5), is reversible and mediated by specific hormone receptors.
Area of Science:
- Biochemistry
- Metabolic Regulation
- Adipose Tissue Biology
Background:
- Glycogen synthesis is crucial for energy storage in adipose tissue.
- Regulation of glycogen synthase activity is complex and involves multiple forms.
- Understanding hormonal control of glycogen synthase is key to metabolic research.
Purpose of the Study:
- To test the hypothesis that interconversion between glucose-6-phosphate-dependent forms of glycogen synthase regulates glycogen synthesis in adipose tissue.
- To determine the role of glucose-6-phosphate-dependent forms in glycogen synthase regulation.
- To investigate the hormonal control mechanisms influencing glycogen synthase interconversion.
Main Methods:
- Assessing glycogen synthase activity through the activation constant (A0.5) for glucose-6-phosphate.
- Measuring the activity ratio in the presence and absence of glucose-6-phosphate.
- Utilizing insulin and adrenergic agonists (isoproterenol, methoxamine) to study hormonal effects.
- Examining the reversibility of hormone-induced changes in enzyme activity.
Main Results:
- Glycogen synthase interconversion in adipose tissue primarily involves glucose-6-phosphate-dependent forms.
- The activation constant (A0.5) for glucose-6-phosphate is a more sensitive measure of interconversion than the activity ratio.
- Insulin decreased A0.5, while epinephrine increased it, without significantly altering the activity ratio.
- Insulin's effect on A0.5 occurred independently of hexose transport, and beta-adrenergic receptors mediated epinephrine's effect.
Conclusions:
- Glycogen synthesis in adipose tissue is catalyzed by multiple glucose-6-phosphate-dependent forms of glycogen synthase.
- Hormones regulate glycogen metabolism by inducing reversible interconversions between these enzyme forms.
- No evidence supports the existence of a glucose-6-phosphate-independent form of glycogen synthase in intact adipose tissue.