Kinetics of oxygen-18 exchange between inorganic phosphate and water catalyzed by myosin subfragment 1, using the 18O shift in 31P NMR

J Biol Chem. 1978 May 10;253(9):2908-11.


The time course of oxygen-18 exchange between [18O]Pi and normal water, catalyzed by myosin subfragment 1 in the presence of MgADP, was followed using the shift in 31P NMR caused by the presence of oxygen-18 bound to the phosphorus. Essentially all molecules of [18O]Pi that bind to the enzyme undergo complete exchange and are released as [16O4]Pi. Exchange probably occurs by formation of myosin.ATP from a myosin.ADP.Pi complex and is rapid relative to release of Pi from this complex. The kinetics of exchange give a value for the rate constant for binding Pi to myosin.ADP of 0.23 M-1 S-1 (pH 8.0, 22 degrees C). This value is consistent with exchange occurring by reversal of the ATP-ase reaction back to the myosin.ATP complex.

MeSH terms

  • Animals
  • Kinetics
  • Magnetic Resonance Spectroscopy
  • Mathematics
  • Muscles
  • Myosins* / metabolism
  • Oxygen Isotopes
  • Phosphates
  • Rabbits
  • Water


  • Oxygen Isotopes
  • Phosphates
  • Water
  • Myosins