A saturation transfer phosphorus nuclear magnetic resonance study of arginine phosphokinase in the muscle of a marine mollusc

Abstract

The forward and reverse fluxes of arginine phosphokinase were measured in vitro preparations of the phasic adductor muscle of the scallop Argopecten irradians concentricus using saturation transfer 31P-NMR techniques. The respective fluxes were 4.72 ± 1.46 and 6.98 ± 1.58 μmol/s per g wet weight. The forward-to-reverse flux ratio was near unity, indicating that the arginine phosphokinase reaction is near equilibrium under resting conditions. 31P-NMR spectra showed no evidence of ADP in scallop muscles. Using an experimentally determined apparent equilibrium constant for arginine phosphokinase, the free ADP level was estimated to be 51 nmol/g wet wt. It appears that at least 90% of the ADP pool is bound in this muscle.