Phosphorus nuclear-magnetic-resonance studies of the transition-state analogue complex of creatine kinase

31P nuclear-magnetic-resonance spectra of MgADP bound to creatine kinase in the presence of creatine NO3- ions show that there are two non-identical forms of the bound nucleotide. The sites have different affinities for the nucleotide. MgADP at the high-affinity site is in slow exchange (k less than 125s-1 at 27 degrees C) with free MgADP.