UCLA

Analysis of saturation recovery data from spin-labeled proteins is extended to include the amplitudes in addition to the recovery rates for two-site exchange. It is shown that the recovery amplitudes depend strongly on the exchange rate between states as well as their populations and this dependence provides a simple criterion to identify exchange rates in the 10–1000 kHz range. Analysis of experimental SR relaxation curves via the uniform penalty (UPEN) method allows for reliable identification of single, double, or other multiple-component traces, and global fitting of a set of relaxation curves using both relaxation rates and amplitudes determined from the UPEN fits allows for the estimation of exchange rate in the above domain. The theory is tested on simple model systems, and applied to the determination of conformational exchange rates in spin-labeled mutants of T4 Lysozyme and intestinal fatty acid binding protein. Finally, an example of T1-weighted spectral editing is provided for systems in the slow exchange limit.