Time development of proton nuclear overhauser effects in proteins

Factors affecting the time development of proton nuclear Overhauser effects (NOES) in proteins were investigated. Calculations indicate that a simple approach based on the behavior of two spins can be used to extract values of the cross-relaxation rates, σ, between close protons. This method cannot in general be used to obtain accurate direct relaxation rates, ρ{variant}, because of systematic errors, the origin and magnitude of which are discussed. The power levels needed to achieve limiting rates of NOE development and hence accurate values of the cross-relaxation rates were also considered. Other systematic errors important in the analysis and collection of NOE data are also examined. Experimental results from the tryptophan residues of the protein lysozyme are presented. A detailed analysis of the time development of the NOE for one of the residues is presented and shows many of the features predicted by the calculations. © 1982.