Electron-spin resonance studies of lipid-modified microsomes from Friend erythroleukemia cells

The fatty acid composition of cultured Friend erythroleukemia cells was modified by supplementation of the medium with oleic or linoleic acid. There was a 30% reduction in saturated and a 35% reduction in polyunsaturated fatty acids in microsomal phospholipids when the cells were grown in media supplemented with oleic acid, and a 3-fold increase in polyunsaturated fatty acids when the cells were grown in linoleic acid-supplemented media. Electron-spin resonance studies with the 5-nitroxystearate probe demonstrated that there was no appreciable change in microsomal lipid mobility as measured by the order parameters. In contrast, changes in lipid mobility were detected with the spin-label probe when microsomes were first isolated from Friend erythroleukemia cells and subsequently modified by incubation with liposomes composed of either dioleoyl- or dilinoleoylphosphatidylcholine plus bovine liver phospholipid-exchange protein. The fatty acid compositional changes produced in these microsomes were similar to those obtained when the intact cells were grown in media containing supplemental fatty acids. These findings indicate that the lipid mobility of Friend cell microsomes can be altered by phospholipid replacements in vitro, but that this does not occur when similar microsomal fatty acid modifications are produced during culture of the intact cell.