A Raman spectroscopic investigation of the lipid state in acetylcholine receptor-rich membranes from Torpedo marmorata.

The lipid state in acetylcholine receptor (AcChR)-rich membranes purified from electric organ of Torpedo marmorata was studied in the temperature interval from 0 degrees C to 35 degrees C using the (C-H) stretching and (C-C) skeletal optical vibrations. The Raman spectra of AcChR-rich membranes, recorded immediately after preparation of the samples, indicate that the lipids are in a predominant triclinic crystalline lattice and do not undergo a phase transition when the temperature increases up to 35 degrees C. However, the polar groups of the lipids appear subject to temperature-induced variations. After extraction of 43-kd and other non-receptor proteins, spectra indicate an order-disorder phase transition of lipids at approximately 21 degrees C. This transition appears less cooperative than the transition of the membrane lipid extract. The role of the proteins in preservation of the crystalline state of lipids in AcChR-rich membranes is discussed.