Transverse 1H cross relaxation in 1H-15N correlated 1H CPMG experiments.

Transverse 1H cross relaxation was observed in Carr-Purcell-Meiboom-Gill (CPMG) experiments by recording 15N-1H correlated spectra of amides in HIV protease that was perdeuterated at nonexchangeable sites. Perdeuteration suppresses 1H-1H J coupling and improves spectral resolution and sensitivity. Measurements of cross-peak intensities, arising from cross relaxation, were made as a function of (i) Deltaf, the frequency difference between the spins, and (ii) tauCPMG, one-half of the duration between CPMG pi pulses. Cross peaks were observed when tauCPMG was less than 1/(2Deltaf), in agreement with theoretical calculations.