Interaction of cholesterol with various glycerophospholipids and sphingomyelin.
The influence of cholesterol on the phase behavior of glycerophospholipids and sphingomyelins was investigated by spin-label electron spin resonance (ESR) spectroscopy. 4-(4,4-Dimethyl-3-oxy-2-tridecyl-2-oxazolidinyl)butanoic acid (5-SASL) and 1-stearoyl-2-[4-(4,4-dimethyl-3-oxy-2-tridecyl-2-oxazolidinyl)butanoy l]-sn- glycero-3-phosphocholine (5-PCSL) spin-labels were employed for this purpose. The outer hyperfine splitting constants, Amax, measured from the spin-label ESR spectra as a function of temperature were taken as empirical indicators of cholesterol-induced changes in the acyl chain motions in the fluid state. The Amax values of 5-PCSL exhibit a triphasic dependence on the concentration of cholesterol for phosphatidylcholines and bovine brain sphingomyelin. We interpret this dependence as reflecting the existence of liquid-disordered, ld, liquid-ordered, lo, and coexistence regions, ld + lo. The phase boundary between the ld and the two-phase region and the boundary between the lo and the two-phase region in the phosphatidylcholine-cholesterol systems coalesce at temperatures 25-33 degrees C above the main-chain melting transition temperature of the cholesterol-free phosphatidylcholine bilayers. In the case of bovine brain sphingomyelin, the ld-lo phase coalescence occurs about 47 degrees C above the melting temperature of the pure sphingomyelin. The selectivity of interaction of cholesterol with glycerophospholipids of varying headgroup charge was studied by comparing the cholesterol-induced changes in the Amax values of derivatives of phosphatidylcholine, phosphatidic acid, phosphatidylethanolamine, phosphatidylglycerol, and phosphatidylserine spin-labeled at the fifth position of the sn-2 chain.(ABSTRACT TRUNCATED AT 250 WORDS)
Sankaram
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MB
Department of Biochemistry, University of Virginia Health Sciences Center, Charlottesville 22908.
Thompson
T E
TE
D002784:Cholesterol / Q000378:metabolism / Q000502:physiology*; D004578:Electron Spin Resonance Spectroscopy; D008560:Membrane Fluidity / Q000502:physiology; D010712:Phosphatidic Acids / Q000378:metabolism*; D010713:Phosphatidylcholines / Q000378:metabolism; D013109:Sphingomyelins / Q000378:metabolism*; D013113:Spin Labels
D010712:Phosphatidic Acids; D010713:Phosphatidylcholines; D013109:Sphingomyelins; D013113:Spin Labels; D002784:Cholesterol