A novel experiment for the quantitative measurement of CSA(H-1(N))/CSA(N-15) cross-correlated relaxation in N-15-labeled proteins

An experiment is presented which allows for the quantitative measurement of the relaxation interference between the H-1(N) CSA and N-15 CSA interactio ns in N-15 labeled proteins. A constant-time buildup scheme is used to meas ure the differential relaxation rate, eta, between double-quantum (DQ) and zero-quantum (ZQ) H-1(N)-N-15 coherences. The CSA/CSA experiment was record ed at three different B-o field strengths. The CSA(H-1(N))/CSA(N-15) cross- correlation rate was obtained from the linear fit of the measured rate, eta , versus B-o(2) for 77 residues of the EH2 domain from mouse Eps15.