ELIMINATION OF CROSS-RELAXATION EFFECTS FROM 2-DIMENSIONAL CHEMICAL-EXCHANGE SPECTRA OF MACROMOLECULES

We demonstrate here a method for eliminating cross-relaxation effects from exchange spectra of macromolecules that permits a more rigorous study of chemical-exchange processes. In the spin diffusion limit, the laboratory-frame cross-relaxationrate is negative and equal to half the rotating-frame cross-relaxation rate, which is positive. If, during the mixing time, the magnetization is flipped rapidly between the two frames such that the average residence time in the NOESY:ROESY framesis 2:1, then the magnetization exchange due to cross-relaxation will cancel out and be removed. Since chemical exchangetakes place steadily, irrespective of the frame of reference, it will contribute to cross-peak volumes in the usual manner. Thisapproach has been applied to the elimination of cross-relaxation effects from the 2D exchange spectrum of a small globularprotein, turkey ovomucoid third domain (6062 Da). The results demonstrate that tyrosine-31 executes ring flips on the millisecondtime scale. © 1990, American Chemical Society. All rights reserved.