DOUBLY SENSITIVITY-ENHANCED 3D TOCSY-HSQC

Recently, strategies for double sensitivity enhancement in heteronucle ar three-dimensional NMR experiments were introduced (Krishnamurthy, V .V. (1995) J: Magn. Reson., B106, 170-177; Sattler et al. (1995) J: Bi omol. NMR, 6, 11-22; Sattler et al. (1995) J. Magn. Reson., BIOS, 235- 242). Since a sensitivity enhancement of a factor 2(1/2) can be achiev ed for each indirect dimension, no spectra can theoretically be enhanc ed up to a factor of 2(((n-1)/2)). We propose and analyze a doubly enh anced three-dimensional TOCSY-HSQC sequence. The application of the do ubly enhanced three-dimensional {N-15,H-1} TOCSY-HSQC sequence is show n for uniformly C-13-/N-15- and N-15-labeled samples of the relatively large Azotobacter vinelandii flavodoxin II (179 amino acids). The mai n factors that contribute to the final signal-to-noise enhancement hav e been systematically investigated. The sensitivity enhancement obtain ed for the doubly enhanced TOCSY-HSQC pulse sequence as compared to th e standard (unenhanced) version is close to the theoretically expected factor of two.