SENSITIVITY ENHANCEMENT OF TRIPLE-RESONANCE PROTEIN NMR-SPECTRA BY PROTON EVOLUTION OF MULTIPLE-QUANTUM COHERENCES USING A SIMULTANEOUS H-1AND C-13 CONSTANT-TIME EVOLUTION PERIOD

Short transverse relaxation times of C-alpha and H-alpha single-quantu m states in proteins reduce signal-to-noise ratios of heteronuclear co rrelation experiments involving transfers of C-alpha and H-alpha coher ences. To overcome this ''short transverse relaxation problem'', we ha ve developed a simultaneous H-1 and C-13 constant-time (sim-CT) hetero nuclear multiple-quantum coherence (HMQC) scheme. New features in this design include: (i) utilization of heteronuclear multiple-quantum coh erences for better transverse relaxation properties, (ii) concatenatio n of proton evolution into the simultaneous H-1 and C-13 constant-time period to eliminate separate time periods for proton evolution, and ( iii) use of simultaneous H-1 and C-13 constant-time to remove resonanc e splitting due to multiple two-and three-bond home-and heteronuclear scalar couplings. This general approach for sensitivity enhancement is demonstrated for the HA(CA)(CO)NH triple-resonance experiment. Result s on proteins show that, compared with the heteronuclear single-quantu m coherence version of the same experiment, on average the sim-CT HMQC version of HA(CA)-(CO)NH exhibits enhancements of similar to 20%.