Cross-relaxation bottleneck in water-lysozyme proton magnetization exchange

Abstract

The proton spin-lattice relaxation parameters in natural and deuterated lysozyme solutions have been measured as a function of temperature (0-50 degrees C). The variation of the apparent magnitudes of the water proton magnetizations in the solutions with temperature indicates that magnetic coupling mixes protein and water proton magnetizations. The results are consistent with an exchange cross-relaxation model (Hills, B. P., Mol Phys 1992, 76, 489-508) in which the cross-relaxation acts between the labile and nonlabile protons, rather than between water and protein protons. Although this cross-relaxation pathway clearly affects the observed magnetization fractions in this protein solution, its influence on the relaxation rates is less apparent.