¹⁵N T₁ Relaxation Data 

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For spin-lattice R_S(S_z) measurements, an inversion-recovery building block is applied during the relaxation building block. Thus, after an initial refocused INEPT pulse train, the in-phase S magnetization is converted to S_z magnetization by applying a 90 S pulse. During the T period, proton saturation is needed to remove other relaxation mechanisms. After the following T period, another 90 S pulse creates transverse S magnetization which is allowed to evolve during the conventional t₁ period and converted to the desired in-phase ¹H magnetization by a refocused retro-INEPT pulse train.

Several approaches have been described to measure ¹⁵N T₁ relaxation data ( 89BIO8972 , 90BIO4394 , 92BIO5269 , 94JMRA121-111 , 94BIO5984 , 95BIO2408 , 95JMRB279-107 , and 99JB295 ). Recently, TROSY-based approaches show improved sensitivity and resolution for large biomolecules ( 00JMR423-143 ).

Experimental: Two sets of T₁ measurements can be carried out at different fields to estimate statistical errors. Usually about 10 spectra with relaxation delays ranging from 0.02 to 2 seconds are carried out. Peaks heights or integrated peaks can be used to determine the corresponding relaxation rates as a function of spectral dispersion.

Mean T₁ (or R₁) values of some proteins at different fields:

R₁ of 1.2s^-1 at 750 MHz (2s^-1 at 500 MHz) for alpha-sarcin (150 residues) ( 02JB301-24) (correlation time of 7.54 ns, 150 residues)

907 ms at 600 MHz (786 ms at 500 MHz) for CDK inhibitor p19^INK4d (correlation time of 13.6 ns, 166 residues)