The structure and thermotropism of thymocyte plasma membranes as revealed by laser-raman spectroscopy.

1. Plasma membranes from rabbit thymocytes have been analyzed by laser-Raman spectroscopy over the 800-3000 cm-1 region and the spectra compared with those of endoplasmic reticulum, as well as relevant liposome systems. 2. Evaluation of the Amide I and Amide III regions indicates that thymocyte plasma membranes, but not endoplasmic reticulum, contain appreciable beta-structure peptide. This conclusion is supported by infrared spectroscopy. 3. Evaluation of the 2890 cm-1: 2850 cm-1 intensity ratio of plasma membranes as a function of temperature, using an integration technique, demonstrates a thermotropic lipid transition centered near 23 degrees C. This transition is less sharp than one observed with egg lecithin in this temperature range. 4. The significance of the thermotropic transition is evaluated in view of the lack of thermotropic lipid-protein segregation detectable by freeze-fracture electron microscopy (Wunderlich, F., Wallach, D.F.H., Speth, V. and Fischer, H. (1973) Biochim. Biophys. Acta 373, 34-43).