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The polysome as a terminal for the creatine phosphate energy shuttle
F Savabi1, C L Carpenter, C Mohan
1Department of Pharmacology and Nutrition, University of Southern California, School of Medicine, Los Angeles 90033.
Biochemical Medicine and Metabolic Biology
|December 1, 1988
Summary
The creatine phosphate shuttle powers muscle protein synthesis in rat muscle polysomes. Bound creatine kinase regenerates ATP and GTP, supporting energy transport via creatine phosphate.
Area of Science:
- Biochemistry
- Molecular Biology
- Muscle Physiology
Background:
- The creatine phosphate (CP) shuttle is crucial for energy transfer in muscle.
- Its role in protein synthesis energetics within isolated polysomes requires further elucidation.
Purpose of the Study:
- To investigate the function of the CP shuttle in muscle protein synthesis energetics.
- To determine if polysomes possess bound creatine kinase activity for ATP regeneration.
Main Methods:
- Isolated rat hindlimb muscle polysomes were prepared and assayed for creatine kinase activity.
- Amino acid incorporation was measured using [3H]leucine under different energy regeneration conditions (CP vs. exogenous ATP system).
- Phosphate transfer from [33P]creatine phosphate to GTP was monitored.
Main Results:
- Polysomes exhibited bound creatine kinase activity (38 mU/mg RNA).
- CP significantly enhanced amino acid incorporation compared to an exogenous ATP regenerating system, indicating efficient endogenous ATP regeneration.
- Evidence suggests nucleoside diphosphokinase activity associated with polysomes facilitates GTP phosphorylation by CP.
Conclusions:
- Skeletal muscle polysomes possess bound creatine kinase, acting as terminals for the CP energy shuttle.
- CP regenerates GTP, likely via nucleoside diphosphokinase, supporting protein synthesis.
- These findings support enzyme compartmentation and the role of CP, not ATP, as the primary energy transport form in muscle.