MEASUREMENT OF C-13(ALPHA)-(CO)-C-13 CROSS-RELAXATION RATES IN N-15-(IC)-C-13-LABELED PROTEINS

Internal motions play an important role in the biological function of proteins and NMR relaxation studies may characterize them over a wide range of frequencies. An experimental pulse scheme is proposed for the measurement of the (CO)-C-13-C-13(alpha) cross-relaxation rate. For s ensitivity reasons, this measurement is performed in an indirect manne r through several coherence transfer steps, which should thus be calib rated independently. Contributions of other relaxation pathways can be eliminated by the determination of the initial slope of the buildup c urve. The cross-relaxation rates have been determined on a N-15-/C-13- labelled 116-residue protein and the significant variations along the sequence have been interpreted as evidence of an increased amount of f ast local motion.