31P nuclear magnetic resonance and freeze-fracture electron microscopy studies on Escherichia coli. I. Cytoplasmic membrane and total phospholipids.

1. At the growth temperature the total phospholipids isolated from Escherichia coli cells give rise to 31P-NMR spectra which indicate the existence of lamellar, isotropic and hexagonal phases. These phases are also detected by freeze fracture electron microscopy. In particular, the isotropic phase may contain lipidic particles (possibly inverted micelles) associated with the lamellar phase. 2. The cytoplasmic membrane isolated from E. coli cells grown at 37 degrees C is mainly lamellar at 25 degrees C, whereas at 37 and 45 degrees C the presence of some almost isotropic phospholipid motion is indicated. The possible significance of the isotropic phase for the functioning of the cytoplasmic membrane is discussed.