P-31 NMR SATURATION-TRANSFER STUDY OF THE CREATINE-KINASE REACTION INHUMAN SKELETAL-MUSCLE AT REST AND DURING EXERCISE

The creatine kinase reaction has been studied by P-31 NMR in exercisin g human calf muscle, Quantitative analysis of high energy phosphates a nd saturation transfer study of the creatine kinase flux in the direct ion of ATP synthesis (V-for) were performed at rest and during exercis e. As expected, exercise induced a [PCr] decrease (from 28.5 +/- 0.9 t o 21.9 +/- 1.5 mM, P < 0.01) matched by a P-i increase (from 4.5 +/- 0 .2 to 8.9 +/- 1.8 mM, P = 0.06). pH(i) and [ATP] remained unchanged. V -for did not change from rest (12.4 +/- 0.9 mM s(-1)) to moderate exer cise and decreased at the highest exercise level (8.4 +/- 1.4 mM s(-1) , P = 0.006). This observation differs from the prediction of the crea tine kinase rate equation, showing an increase in the flux with exerci se intensity, computations suggest that this discrepancy arises from m etabolite compartmentalization and/or from the reaction kinetics of a dead end complex stabilized by planar anions.