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Modulation of phosphorylase kinase activity by sphingolipids
L G Baltas1, V G Zevgolis, S M Kyriakidis
1Institute of Biological Research, National Hellenic Research Foundation, Athens, Greece.
Biochemistry International
|July 1, 1989
Summary
Psychosine (galactosyl sphingosine) inhibits rabbit skeletal muscle phosphorylase kinase activity. Gangliosides, particularly GD1a, stimulate this kinase, especially at low calcium concentrations.
Area of Science:
- Biochemistry
- Enzymology
- Signal Transduction
Background:
- Skeletal muscle phosphorylase kinase (PhK) is a key regulator of glycogenolysis.
- Understanding PhK regulation by lipids is crucial for metabolic research.
Purpose of the Study:
- To investigate the effects of psychosine and various gangliosides on rabbit skeletal muscle phosphorylase kinase activity.
- To elucidate the modulatory roles of specific glycosphingolipids in PhK regulation.
Main Methods:
- Enzyme activity assays were performed at different pH values (6.8 and 8.2).
- The effects of psychosine, sphingosine, and various gangliosides (GD1a, GT1b, GM1, GM3) on PhK were assessed.
- Autophosphorylation and autoactivation rates were monitored.
Main Results:
- Psychosine potently inhibited both nonactivated and activated PhK.
- Sphingosine showed weaker inhibition at pH 6.8; other sphingolipids were ineffective.
- Gangliosides, especially GD1a, stimulated nonactivated PhK, with GD1a significantly enhancing activity at low Ca2+.
- Both psychosine and GD1a promoted alpha-subunit autophosphorylation, but psychosine blocked autoactivation, while GD1a enhanced it.
Conclusions:
- Psychosine acts as a potent inhibitor of rabbit skeletal muscle phosphorylase kinase.
- Specific gangliosides, notably GD1a, function as activators, modulating PhK activity and Ca2+ sensitivity.
- These findings highlight the complex regulatory roles of glycosphingolipids in phosphorylase kinase function.