31P-NMR spectrum of phosphocreatine: Deuterium-induced splitting of the signal

It has been found in experiments with high resolution 31P-NMR spectroscopy (200 MHz) that the phosphocreatine peak is splitted into two different peaks in the mixtures of H2O and D2O and is single but with different chemical shifts in pure H2O and D2O. This phenomenon is explained by substitution of protons of guanidino group in phosphocreatine by deuterium. The effect of splitting disappeared at extreme pH values (>8.5 or <4.0) and at temperatures higher than 45°C due to accelerated proton-deuterium exchange. Creatine kinase added to phosphocreatine solution also lowered its temperature of peaks' collapse by 5°–10°C. A saturation (spin) transfer method was used to show that the phosphoryl group transfer to ADP in creatine kinase active center is slower with deuterium-substituted phosphocreatine than with H-phosphocreatine. The data are taken to show the importance of the proton transfer step in the creatine kinase reaction mechanism and acceleration of phosphocreatine proton-deuterium exchange by creatine kinase.