Rotational Inhibition and Magnetization Transfer in α-Crystallin Solutions

The magnetic field dependence (dispersion profile) of 1/T1 of solvent water protons of solutions of the mammalian eye lens protein α-crystallin has a reversible nonlinear dependence on concentration which, as protein concentration increases above ∼20 wt.%, changes rapidly from a profile characteristic of mobile protein solute to a profile characteristic of rotationally immobilized protein (e.g., chemically cross-linked). From quantitative comparisons of new measurements of K at 200.1 MHz, the rate of water-to-protein interfacial magnetization transfer, with earlier data for α-crystallin and bovine serum albumin (BSA), we conclude, for α-crystallin, that: (i) Brownian rotation is slowed by intermolecular interactions at unexpectedly low concentrations; (ii) K is mediated by the newly reported, long-lived, protein hydration sites with the same surface density as BSA; and (iii) 14N peaks seen in solvent 1/T1 arise from interfacial magnetization transfer plus diffusion to protein NH magnetization sinks. © 1993 Academic Press, Inc.