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 an d a set of n-(9-anthroyloxy)stearate (n=2,7 and 12) probes were measur ed by using differential polarized phase fluorometry in whole membrane s and in protein-free liposomes prepared with the total lipid extracts of rat liver microsomes and erythrocyte membranes. For the anthroylox ystearate probes, two rotational modes, ''in'' and ''out'' of the plan e of the anthroyl aromatic ring, were partially resolved by measuring at different excitation wavelengths. A more ordered structure sensed b y all these probes and a higher viscous resistance to the ''out of the plane'' motion of 7- and 12-anthroyloxystearates is found in erythroc yte compared with microsomal protein-free systems. In both erythrocyte membranes and microsomes, proteins impose a hindrance to the diphenyl hexatriene wobbling motion reducing its range and to a lesser extent a lso its rate. Membrane proteins also hinder the ''out of the plane'' m otion, which is unhindered in the protein-free systems, mainly for the 2- and 7- anthroyloxystearate probes in both microsomal and erythrocy te membranes. However, for the ''in the plane'' rotation of the 2-, 7- and 12-anthroyloxystearates, proteins decrease the range without modi fying the rate in microsomes, but they increase both, range and rate i n erythrocyte membranes. Moreover, proteins decrease the viscous resis tance for the ''out of the plane'' rotation of all the anthroyloxy-ste arates in erythrocyte membranes, but increase it for this rotational m ode of the anthroyl group attached to the 7- and 12- positions in micr osomes. These results indicate that the effect of membrane proteins on the structural and dynamical properties of the lipid matrix depends o n the kind of proteins and/or on the lipid phase composition.