Skeletal Muscle Metabolism
ATP is required in skeletal muscle tissue to power the contraction cycle and to pump Ca ++ back into the sarcoplasmic reticulum following muscle contraction.
There are 3 methods of producing ATP in muscle tissue:
Creatine Phosphate
The ability to produce ATP by using creatine phosphate is unique to muscle fibres. Creatine phosphate is a compound that is found only in muscle cells. It is responsible for storing any excess ATP produced while the body is at rest. When muscle fibres are at rest (relaxed), they produce more ATP than they need for resting metabolism. The excess ATP is used to synthesize Creatine Phosphate an energy-rich molecule. The enzyme Creatine Kinase (CK) catalyzes the transfer of one of the high-energy phosphate groups from ATP to Creatine forming Creatine Phosphate. Creatine is a small amino acid like molecule that is made in the liver, kidneys, and pancreas and then transported to muscle fibres. Creatine Phosphate is 3-6x more plentiful than ATP in the sarcoplasm of a relaxed muscle fibre. When contraction begins and ADP levels rise, the enzyme Creatine Kinase (CK) catalyzes the transfer of a high-energy Phosphate group from creatine phosphate back to ADP (phosphorylation). This quickly regenerates new ATP molecules.
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