The analysis of NMR relaxation data in terms of multiple internal motions

A novel formalism for estimating the complex motions of proteins and other flexible macromolecules from NMR relaxation measurements is applied to ¹³C NMR relaxation data on the Bovine Pancreatic Trypsin Inhibitor (M. W. 6,500). Six experimental parameters measured at two field strengths are accounted for by a minimum of three motions at each carbon group. Low frequency components make small but finite contribution to the relaxation of all resonances, suggesting a general low frequency distortion of the backbone. Rotational diffusion of the protein makes a relatively minor contribution to the relaxation process. For aliphatic groups, rotation of side chains dominates relaxation.