A quantitative J-correlation experiment for the accurate measurement of one-bond amide 15N-1H couplings in proteins

Very precise measurements of 1JNH couplings have been made for approximately 40% of the amide sites in cyanometmyoglobin using two different experimental approaches. The first approach is a previously described frequency-based method in which the couplings are observed as splittings in the frequency-domain spectrum. The second is a new approach, along the lines of quantitative J-correlation spectroscopy, in which the coupling is encoded in the resonance intensity. Measurements obtained from the two experimental techniques are in agreement to a high degree of precision (s.d. of 0.17 Hz) and residual deviations appear to be largely random. The new method offers substantial time savings when resonances are widely dispersed in the frequency domain and may offer improved precision in these instances.