TRANSMEMBRANE F-19 NMR CHEMICAL-SHIFT DIFFERENCE OF FLUORINATED SOLUTES IN LIPOSOMES, ERYTHROCYTES AND ERYTHROCYTE-GHOSTS

In erythrocytes suspended in isotonic medium, a number of fluorinated anions showed well resolved F-19 NMR resonances from the solute populations in the intra- and extracellular compartments; the intracellular resonances were shifted to higher frequency (low field). In addition F-19 NMR resonances of extracellular solutes were shifted to higher frequency when bovine serum albumin was incorporated into the extracellular medium. The dependence of F-19 NMR chemical shift on protein concentration was also demonstrated using resealed red cell ghosts and liposomes; in the presence of external hemoglobin, lysozyme and bovine serum albumin, the shift of the external resonances was to higher frequency. In addition, significant high frequency shifts of F-19 NMR resonances were evident along with an increase of temperature. The results of the present study further support the contention that the principal physical basis for the shifts is the disruption of direct hydrogen bonds between F-19 of the solutes and (primarily) solvent H2O by protein hydration. The 'split peak' phenomenon is of general importance in biological systems where a transmembrane protein-concentration difference exists.