Infrared spectroscopic studies of Acholeplasma laidlawii B membranes: comparison of the gel to liquid-crystal phase transition in intact cells and isolated membranes

The physical state of the membrane lipids in the plasma membranes of intact, live Acholeplasma laidlawii B cells was probed by Fourier‐transform infrared spectroscopy and compared with that in isolated membranes. Infrared spectra of live A. laidlawii B cells, enriched biosynthetically in the presence of avidin, with saturated deuterated and unsaturated non‐deuterated fatty acids have been recorded at a variety of temperatures. The results indicate that within the temperature range of the gel to liquid‐crystal phase transition, the live cells are able to keep the ‘fluidity’ of their plasma membranes at a considerably higher value compared to that in the isolated membranes at the same temperature. While this is a generally valid observation, the degree by which live and isolated membranes differ in their liquid‐crystal‐phase content at a given temperature depends on the nature of the exogenous fatty acid and the temperature of growth.