AN OFF-RESONANCE ROTATING-FRAME RELAXATION EXPERIMENT FOR THE INVESTIGATION OF MACROMOLECULAR DYNAMICS USING ADIABATIC ROTATIONS

N-15 off-resonance rotating frame relaxation can be applied to the stu dy of internal dynamics in proteins in the millisecond to microsecond regime. We show that the performance of existing methods can be improv ed by application of simultaneous amplitude and phase-modulated adiaba tic RF pulses to align the nuclear spin magnetization with the off-res onance spin-lock field for all the spins under investigation. Applicat ion of this technique to the 269-residue serine protease PB92 allowed the measurement of N-15 off-resonance rotating frame relaxation rates for all nonoverlapping residues in the protein, including the arginine side chains, encompassing a chemical shift range of 50 ppm. Simulatio ns indicate that by use of the proposed adiabatic RF pulses rotating f rame relaxation rates can be obtained for magnetization vectors aligne d at arbitrary angles with the static field. (C) 1998 Academic Press.