Muscle energy metabolism in human phosphofructokinase deficiency as recorded by 31P nuclear magnetic resonance spectroscopy.

31P nuclear magnetic resonance studies of a patient with phosphofructokinase deficiency in muscle provided the following new findings: First, ATP metabolism is disturbed at rest and during exercise. At rest, ATP levels are lower than normal and continue to decline during exercise. Second, exercise kinetics are normal, suggesting a normal mitochondrial fuel supply although glycolysis is blocked. Third, no "phosphate trapping" is observed during prolonged low-level exercise. Fourth, postexercise recovery is abnormally prolonged by the slow dephosphorylation of sugar phosphates, which has an in vivo half-life of about nine minutes. These findings demonstrate how muscle tissue adapts to a block in a major bioenergetic pathway.