Direct observation of the phase behavior of the lipid bilayers of phage PM2 and the intact host cells by 1H-31P cross-polarization NMR.

A method for obtaining the 31P NMR spectrum of a particular supramolecular structure in an intact biological system was developed by applying the 1H-31P cross-polarization technique to a lipid-containing bacteriophage, PM2, and its host bacterium, Alteromonas espejiana. It was shown that 31P NMR spectra of nucleic acids and lipid bilayers can be obtained separately with short and long thermal contact times, respectively. The temperature dependence of the chemical shift anisotropy (delta sigma = sigma parallel - sigma perpendicular) was examined for the separately obtained membrane spectra. Referring to the results of thermal analysis and 31P NMR spectra of bilayers of the extracted phospholipids, the phase transition of the biomembrane was identified for the PM2 phage and the host cell. The dynamic state of the biomembrane of the intact bacterium was directly monitored in detail. The phase behavior of the PM2 lipid bilayer showed good agreement with the earlier report (Akutsu et al., 1980). It turned out that the phase behavior of the intact biomembrane is different from that of the bilayer of the extracted lipids for both PM2 and the host cell. Namely, the terminal temperatures of the phase transition of the host cell and PM2 membranes were lower and higher than those of the extracted phospholipids, respectively.