文摘
A quantitative J-correlation pulse sequence is described that allows simultaneous determination of one-bond and two-bond nitrogen-carbon coupling constants for protonated or deuterated proteins. Coupling constants are calculated from volume ratios between cross peaks and reference axial peaks observed in a single 3D spectrum. Accurate backbone 1JNC′, 1JNC&agr;, and 2JNC&agr; coupling constants are obtained for the two [15N;13C]-labeled, medium-sized proteins flavodoxin and xylanase and for the [2H;15N;13C]-labeled, large protein DFPase. A dependence of one-bond and two-bond JNC&agr; values on protein backbone &psgr; torsion angles is readily apparent, in agreement with previously found correlations. In addition, the experiment is performed on isotropic as well as aligned protein to measure associated 15N-13C residual dipolar couplings.