RAPID PUBLICATIONS Disruption of the Purine Nucleotide Cycle A POTENTIAL EXPLANATION FOR MUSCLE DYSFUNCTION IN MYOADENYLATE DEAMINASE DEFICIENCY

fatigability, postexercise myalgias, and delayed re-covery of muscle strength after activity is described. Skeletal muscle from this patient had <1.0 % normal myoadenylate deaminase activity and NH3 was not released from muscle after ischemic exercise. In association with this enzyme deficiency, exercise led to a>90 % reduction in muscle content of adenine nucleotides. No inosine monophosphate accumulated after exercise and total purine content of the muscle fell to 21 % of control. Repletion of the adenine nucleotide pool in this patient was delayed compared to controls, and ATP content had only returned to 68 % of control at 165 min after exercise. These studies demonstrate that disruption of the purine nucleotide cycle as a consequence of myoadenylate deaminase deficiency results in marked alterations in ATP con-tent of muscle, and potentially, these changes in ATP content could account for muscle dysfunction in this patient