Phosphocreatine is a high energy compound in the skeletal muscle of vertebrates and is present in 4 to 5 times the concentration of ATP.
Reference: Saks 2000 Acta Physiol Scand
The high-energy phosphate group of phosphocreatine is rapidly transferred to ADP by the action of creatine kinase and the following reaction occurrs:
- Phosphocreatine + ADP ↔ creatine + ATP
ATP formation is favored at the expense of phosphocreatine. This fact explains why the ATP concentration of muscle does not decline during a single contraction: the terminal phosphate group lost from ATP during the contraction is instantly replenished at the expence of phosphocreatine.
If the muscle is stimulated for longer periods in the absence of glycolysis or respiration, the phosphocreatine supply will eventually become depleted. Only then the ATP concentration will decline.
MitoPedia topics: Substrate and metabolite