COMPARISON OF WATER RELAXATION-TIME IN SERUM-ALBUMIN SOLUTION USING NUCLEAR-MAGNETIC-RESONANCE AND TIME-DOMAIN REFLECTOMETRY

We measured the nuclear magnetic resonance (NMR) relaxation times T-1 and T-2 of water in an albumin solution and compared them with values calculated using dielectric relaxation parameters obtained by time domain reflectometry (TDR) and translational diffusion coefficients obtained by NMR. The calculated NMR relaxation times reproduced well the observed values. in a globular protein, three kinds of rotational relaxation parameters are observed by TDR method; these can be assigned to the protein, the bound water, and the free water rotations. The observed NMR relaxation time constitutes, however, a single component, indicating that the extreme narrowing condition is met and free; bound, and next-to-bound water molecules are exchanging rapidly on the NMR time scale. The NMR relaxation times T-1 and T-2 are, however, not equal to one another for the same albumin solution. Since low-frequency fluctuating field inhomogeneity affects T-2, our results suggest that the long correlation time associated with the overall rotation of albumin is a main fraction in the transversal water relaxation mechanism.