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

Abstract

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.

Molecules in Physics, Chemistry, and Biology

“…Two other shoulders are observed near 2855 and 2880 cm-I which have been assigned to the symmetric (v s CH 2 ) and asymmetric stretching (v a CH 2 ) vibrations of the lipid methylene chains [133]. Increasing temperature does not perturb the conformation of the membrane components since there are no changes in intensity and frequency of the protein and lipid vibrations [159]. The spectrum in Fig.…”

“…In the spectra of both samples, the lipid asymmetric vibration (v aCH2) appeared at the normal vibration frequency (near 2885 cm-I ), but symmetric stretching band appeared at higher frequency in the samples used immediately after the preparation (near 2862 cm-I instead of 2855 cm-I ) [159]. In the spectra of both samples, the lipid asymmetric vibration (v aCH2) appeared at the normal vibration frequency (near 2885 cm-I ), but symmetric stretching band appeared at higher frequency in the samples used immediately after the preparation (near 2862 cm-I instead of 2855 cm-I ) [159].…”

“…The spectrum in Fig. The absence of the modification in the intensity of the lipid asymmetric stretching vibrations at 2880 cm-I [159] indicates that phase transition does not take place in the postsynaptic membrane lipids in this temperature range. Increasing temperature does not perturb the conformation of the membrane components since there are no changes in intensity and frequency of the protein and lipid vibrations [159].…”

“…Fortunately, the 2800-3100 cm -1 region was free of the fluorescence and thus, in our earlier work, only this region has been analysed [158,159]. Raman spectra of these samples were always accompanied by a very high fluorescence background which obscured almost all vibrations in the 400-1800 cm-1 spectral range.…”

Raman spectroscopic study on the conformation of 11 S form acetylcholinesterase from Torpedo californica

“…To date, studies have been conducted on the conformation of the chemical transmitter, acetylcholine and some of its analogues [1][2][3][4], as well as on postsynaptic membranes from the Torpedo rnarmorata electric organ enriched in acetylcholine receptor, and the isolated receptor molecule [5,6]. Continuing this approach an examination of the Raman spectra of acetylcholinesterase (ACHE) was undertaken to identify specific features in the conformation of the enzyme and to provide a quantitative estimation of its secondary structure.…”