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Updated: Aug 17, 2026
Using a GFP-tagged TMEM184A Construct for Confirmation of Heparin Receptor Identity
Published on: February 17, 2017
Novel heparin-activated protein kinase activity in rabbit skeletal muscle
Abstract:
A heparin-activated protein kinase has been identified in rabbit skeletal muscle. The enzyme, which had a native molecular mass of 70 kDa as judged by gel filtration, was stimulated 3- to 5-fold by heparin, half-maximally at 3 micrograms/ml heparin. The stimulation by heparin was not reproduced by other polyanions such as polyaspartate and polyglutamate. The protein kinase was detected by its ability to phosphorylate glycogen synthase; it was ineffective in phosphorylating caseins, phosvitin, histone, or phosphorylase. Glycogen synthase was phosphorylated to a stoichiometry of 0.7-0.8 phosphates/subunit, exclusively at serine residues located in the COOH-terminal CNBr-fragment of the subunit, with a corresponding reduction in the -/+ glucose-6P activity ratio from 0.96 to 0.43. The activity of the protein kinase was unaffected by the presence of Ca2+ and/or phospholipid, cyclic AMP or heat-stable inhibitor protein of cyclic AMP-dependent protein kinase. The enzyme was inhibited about 60% by the presence of glycogen, half-maximal effect at 25 micrograms/ml. The heparin-activated protein kinase is clearly distinguishable from other known glycogen synthase kinases.
Insights
Researchers discovered a novel heparin-activated protein kinase in rabbit skeletal muscle that specifically phosphorylates glycogen synthase. This enzyme is distinct from other known glycogen synthase kinases, offering new insights into muscle glycogen regulation.
Area of Science:
- Biochemistry
- Enzymology
- Muscle Physiology
Background:
- Glycogen synthase is a key enzyme in glycogen synthesis.
- Regulation of glycogen synthase activity is crucial for cellular energy homeostasis.
- Specific protein kinases play vital roles in modulating glycogen synthase function.
Purpose of the Study:
- To identify and characterize a novel heparin-activated protein kinase in rabbit skeletal muscle.
- To investigate the substrate specificity and regulatory properties of this enzyme.
- To determine if this kinase is involved in glycogen synthase regulation.
Main Methods:
- Gel filtration chromatography to determine molecular mass.
- Enzyme activity assays using glycogen synthase and other proteins as substrates.
- Characterization of enzyme kinetics with varying heparin concentrations.
- Analysis of phosphorylation sites on glycogen synthase using peptide mapping.
Main Results:
- A 70 kDa heparin-activated protein kinase was identified in rabbit skeletal muscle.
- The enzyme specifically phosphorylated glycogen synthase at serine residues, reducing its activity.
- Heparin significantly stimulated the kinase, with other polyanions showing no effect.
- Enzyme activity was independent of Ca2+, phospholipids, cAMP, and inhibitor proteins but was inhibited by glycogen.
Conclusions:
- A novel heparin-activated protein kinase distinct from known glycogen synthase kinases has been characterized.
- This enzyme plays a specific role in phosphorylating and regulating glycogen synthase in skeletal muscle.
- The findings provide new molecular insights into the complex regulation of glycogen metabolism.
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