H-1 MAGNETIC CROSS-RELAXATION BETWEEN MULTIPLE SOLVENT COMPONENTS ANDROTATIONALLY IMMOBILIZED PROTEIN

Magnetic cross-relaxation spectra or Z-spectra are presented for water , acetone, methanol, dimethylsulfoxide, and acetonitrile in cross-link ed bovine serum albumin gels. Each solvent studied, reports the same Z -spectrum linewidth and shape for the solid component that follows fro m solutions of the coupled relaxation equations. The Z-spectra demonst rate competition among solvents for specific protein binding sites. Th e rate of magnetization transfer in the rotationally immobilized prote in environment is approximated by 1/T-2 for the solid component, which is shown to account for the observed magnetization transfer rates in the systems studied. The temperature dependence of the Z-spectra are d ifferent for water compared with the organic solvents. The cross-relax ation efficiency in the organic solvents decreases with increasing tem perature because molecules bind less well at high temperature. For wat er, the hydrogen exchange path becomes increasingly important relative to the whole molecule path with increasing temperature, which improve s the net cross-relaxation efficiency.