SYSTEMATIC BIAS IN THE MODEL-FREE ANALYSIS OF HETERONUCLEAR RELAXATION

Several theoretical and practical aspects of the use of heteronuclear relaxation to characterize the internal motion of biomacromolecules are examined. The treatment is cast in the terms of the popular model-free theory of G. Lipari and A. Szabo (J. Am. Chem. Soc.104, 4546 (1982)). In particular, the measurement of longitudinal relaxation in fully coupled systems is found to systematically bias obtained generalized order parameters. It is concluded that it is generally appropriate to utilize an experimental approach which ensures that heteronuclei are decoupled frorn bonded protons during sampling of relaxation. This restricts the types of experiments that can be used to sample relaxation by indirectly detected two-dimensional spectroscopy. The influence of a limited sampling of relaxation, typically required by practical limitations when two-dimensional spectroscopy is employed, is also examined. Finally, the relative importance of T1 and NOE in determining model-free parameters is explored in conjunction with the impact of commonly used assumptions on the analysis. © 1991.