Fluorine-19 nuclear magnetic resonance studies of lipid fatty acyl chain order and dynamics in Acholeplasma laidlawii B membranes. A physical, biochemical, and biological evaluation of monofluoropalmitic acids as membrane probes.

Abstract

Fluorine-19 nuclear magnetic resonance spectroscopy offers a number of unique advantages for studies of lipid fatty acyl chain order and dynamics in model and biological membranes. However, the germinal difluoromethylene fatty acids commonly employed as 19F membrane probes appear to appreciably perturb the organization of model membranes and biomembranes. We have thus synthesized a series of specifically labeled monofluoropalmitic acids and evaluated these as suitable membrane probes. Differential scanning calorimetric studies of aqueous dispersions of several bis-(monofluoropalmitoyl)phosphatidylcholines reveal that a fluorine substitution near the carbonyl group of palmitic acid has only a modest effect on the thermotropic phase behavior of these model membranes and that substitutions in the center or toward the methyl terminus are relatively nonperturbing. Moreover, all bis(monofluoropalmitoyl)phosphatidylcholines tested exhibit nearly ideal mixing in all proportions with dipalmitoylphosphatidylcholine. The thermotropic phase behavior of membranes of the simple, cell-wall-less prokaryote Acholeplasma laidlawii B is also not detectably altered by the presence of appreciable amounts of biosynthetically incorporated monofluoropalmitic acid. We also find that the biosynthetic incorporation of even large amounts of monofluoropalmitic acids into the membrane lipids of A. laidlawii B has no effect upon the growth and survival of this organism. The presence of exogenous monofluoropalmitic acids in the growth medium does not alter the polar head group composition or lipid/protein ratio of the A. laidlawii B membrane. In addition, all monofluoropalmitic acids tested are biosynthetically incorporated as well as palmitic acid itself and distribute relatively evenly between the various membrane glyco- and phospholipids.(ABSTRACT TRUNCATED AT 250 WORDS)