J. Biol. Chem., Vol. 261, Issue 16, 7204-7214, 06, 1986
Influence of sterol structure on phospholipid phase behavior as detected by parinaric acid fluorescence spectroscopy
C Rujanavech, PA Henderson and DF Silbert
Phospholipid-sterol interactions were investigated using parinaric acid
fluorescence spectroscopy. Cholesterol and cholesterol analogues which were
modified in the sterol nucleus or side chain were added at 50 mol % to
multilamellar vesicles of model phospholipids selected to be representative
of major components in an LM cell plasma membrane. These included
sphingomyelins and saturated and monounsaturated phosphatidylcholines and
phosphatidylethanolamines. Based on the changes in cis-parinaric acid
steady-state fluorescence polarization observed with addition of sterol, 50
mol % cholesterol abolished the phase transition of all the model
phospholipids. Dihydrocholesterol and trans-22-dehydrocholesterol behaved
like cholesterol in the two systems studied. 24-Methylcholesterols
interacted well with all phospholipids except phosphatidylethanolamine
which contained an unsaturated fatty acid.
24-Alkyl,trans-22-dehydrocholesterols abolished the phase transition in
only two systems: sphingomyelins and phosphatidylcholines possessing
relatively short saturated acyl chains. Since steady-state anisotropy is a
function of fluorescence lifetime, rotational diffusion rates, and limiting
anisotropy, we determined these parameters for two of the phospholipid
systems. The results show that steady-state anisotropy values for
phospholipid-sterol interactions correlate closely with limiting anisotropy
and to a lesser extent with rotational relaxation time. The behavior of the
sterols in the model phospholipids are used to interpret 1) fluorescence
polarization measurements made with phospholipids extracted from LM cell
plasma membranes, and 2) changes in membrane lipid composition which
accompany growth of LM cells on various sterols.