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 popula tions 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 fre quency when bovine serum albumin was incorporated into the extracellul ar medium. The dependence of F-19 NMR chemical shift on protein concen tration was also demonstrated using resealed red cell ghosts and lipos omes; in the presence of external hemoglobin, lysozyme and bovine seru m albumin, the shift of the external resonances was to higher frequenc y. In addition, significant high frequency shifts of F-19 NMR resonanc es were evident along with an increase of temperature. The results of the present study further support the contention that the principal ph ysical basis for the shifts is the disruption of direct hydrogen bonds between F-19 of the solutes and (primarily) solvent H2O by protein hy dration. The 'split peak' phenomenon is of general importance in biolo gical systems where a transmembrane protein-concentration difference e xists.