INFLUENCE OF MEMBRANE-PROTEINS ON LIPID MATRIX STRUCTURE AND DYNAMICS - A DIFFERENTIAL POLARIZED PHASE FLUOROMETRY STUDY IN RAT-LIVER MICROSOMES AND ERYTHROCYTE-MEMBRANES

The range and rate of the rotation of 1,6-diphenyl-1,3,5-hexatriene and a set of n-(9-anthroyloxy)stearate (n=2,7 and 12) probes were measured by using differential polarized phase fluorometry in whole membranes and in protein-free liposomes prepared with the total lipid extracts of rat liver microsomes and erythrocyte membranes. For the anthroyloxystearate probes, two rotational modes, ''in'' and ''out'' of the plane of the anthroyl aromatic ring, were partially resolved by measuring at different excitation wavelengths. A more ordered structure sensed by all these probes and a higher viscous resistance to the ''out of the plane'' motion of 7- and 12-anthroyloxystearates is found in erythrocyte compared with microsomal protein-free systems. In both erythrocyte membranes and microsomes, proteins impose a hindrance to the diphenylhexatriene wobbling motion reducing its range and to a lesser extent also its rate. Membrane proteins also hinder the ''out of the plane'' motion, which is unhindered in the protein-free systems, mainly for the 2- and 7- anthroyloxystearate probes in both microsomal and erythrocyte membranes. However, for the ''in the plane'' rotation of the 2-, 7- and 12-anthroyloxystearates, proteins decrease the range without modifying the rate in microsomes, but they increase both, range and rate in erythrocyte membranes. Moreover, proteins decrease the viscous resistance for the ''out of the plane'' rotation of all the anthroyloxy-stearates in erythrocyte membranes, but increase it for this rotational mode of the anthroyl group attached to the 7- and 12- positions in microsomes. These results indicate that the effect of membrane proteins on the structural and dynamical properties of the lipid matrix depends on the kind of proteins and/or on the lipid phase composition.