Lipid-protein relationships in erythrocyte membranes revealed by paramagnetic quenching of protein fluorescence

1. Paramagnetic quenching of erythrocyte membrane protein fluorescence by nitroxide-labelled lipid analogues has been studied as a function of temperature and quencher concentration, as well as after cross-linking of membrane proteins by glutaraldehyde. 2. Quenching due to nitroxide stearates reveals a static component, due to binding of quencher molecules to protein, superimposed upon a diffusion-limited component. 3. Static quenching decreases progressively above 35 degree C, a temperature region where a thermotropic discontinuity is known to occur (Bieri, V. G. and Wallach, D. F. H. (1975) Biochim. Biophys. Acta 406, 415-423). 4. Diffusion-limited quenching becomes progressively more prominent as the temperature is raised above 15 degree C. 5. Exposure of membranes to varying concentrations of glutaraldehyde indicates that membrane proteins relatively poorly accessible to cross-linking are those responsible for the membrane thermotropism above 35 degree C. 6. Protein fluorophores accessible to androstane nitroxide are saturated at a low quencher/protein ratio. This ratio is stable below 35 degree C but increases by 50% between 35 and 55 degree C.