Enzymes of the purine nucleotide cycle in muscle of patients with exercise intolerance.

The activities of adenylosuccinate synthetase, adenylosuccinate lyase, and adenosine monophosphate deaminase were measured in muscle from patients suffering from fatigue and cramps following exercise. Results denote the existence of secondary deficiencies of adenylosuccinate synthetase and/or adenylosuccinate lyase in subjects with congenital or acquired myopathies. They also suggest that searches are warranted for primary deficiencies of adenylosuccinate synthetase as a cause of exercise intolerance.