Sensitivity enhancement of HCACO by using an HMQC magnetization transfer scheme

Previous theoretical calculations have demonstrated that the multiquantum r elaxation rate of H-1(alpha)-C-13(alpha)(R-MQ) is, on average, 1.3 +/- 0.4 or 1.7 +/- 0.6 times slower than the single-quantum relaxation rate of C-13 (alpha)(R-c) for a sample with or without, respectively, amide protons. By taking advantage of this fact and by using the PEP sensitivity enhancement scheme, an HMQC version of the HCACO experiment has been developed. We demo nstrate that this new experiment is 23 and 55% more sensitive than the orig inal HSQC version of the HCACO experiment, at constant times of 7 and 27 ms , respectively, for a sample of the BC domain of the ciliary neurotrophic f actor receptor protein dissolved in D2O at 20 degrees C. (C) 2000 Academic Press.