Kinetic isotope effects for fast deuterium and proton exchange rates.

By monitoring the effect of deuterium decoupling on the decay of transverse (15)N magnetization in D-(15)N spin pairs during multiple-refocusing echo sequences, we have determined fast D-D exchange rates kD and compared them with fast H-H exchange rates kH in tryptophan to determine the kinetic isotope effect as a function of pH and temperature.