Multiple thermotropic state transitions in erythrocyte membranes. A laser-Raman study of the CH-stretching and acoustical regions.
1. We have examined the Raman scattering from erythrocyte ghosts at 2700 cm-1 -3000 cm-1 (CH-stretching region), that at low frequencies due to acoustical vibrations, as well as that due to v (-C=C-) and v (=C-C=) of beta-carotene, in the temperature range of -30 degrees C to  +30 degrees C. For comparison we have also evaluated the Rama spectra of liposomes composed of lecithins+/-cholesterol. 2. Plots vs. temperature of the intensities (I) of the approx. 2880 cm-1 and 2932 cm-1 bands relative to the intensity of the thermally stable 2850 cm-1 band, i.e. the (I2880/I2850) and (I2932/I2850) ratios, revealed discontinuities in both erythrocyte membranes and liposomes. 3. In erythrocyte membranes, plots of (I approximately 2880/I2850) and (I approximately 2932/I 2850) reveal several discontinuities. Those reported by (I approximately 2880/I 2850) occur at +17 degrees C and approx. -4 degrees C. The ratio (I approximately 2932/I 2850) reveals a transition between -20 degrees C and +10 degrees C, 1/2 maximal at -8 degrees C. The ratio  (I 1527/I 1158), representing the relative intensity of v (-C=C-) vs. v (=C-C=) of membrane-bound beta-carotene, changes discontinuously with the 17 degrees C transition, but is stable over the rest of the temperature change studied. 4. The data indicate that a major membrane-state transition takes place below 0 degrees C but that an additional transition occurs at approx. 17 degrees C.
D002338:Carotenoids / Q000097:blood; D002462:Cell Membrane / Q000648:ultrastructure*; D002784:Cholesterol; D004530:Egg Yolk; D004912:Erythrocytes / Q000648:ultrastructure*; D005260:Female; D006801:Humans; D007834:Lasers; D008081:Liposomes; D008954:Models, Biological; D010713:Phosphatidylcholines; D012542:Scattering, Radiation; D013057:Spectrum Analysis; D013696:Temperature; D013816:Thermodynamics
D008081:Liposomes; D010713:Phosphatidylcholines; D002338:Carotenoids; D002784:Cholesterol