Fatty acid desaturation in an animal cell mutant defective in plasmanylethanolamine desaturase

Abstract

We have recently reported the isolation of three plasmalogen-deficient mutants in a murine, macrophage-like cell line, RAW 264.7 (Zoeller et al. (1992) J. Biol. Chem. 267, 8299–8306). One of these mutant strains, RAW.12, is deficient in Δ1′-desaturase (plasmanylethanolamine desaturase, EC 1.14.99.19), the activity responsible for introducing the vinyl-ether double bond found in plasmalogens. We have examined these mutant cells to determine whether any of the desaturase activities involved in the desaturation of fatty acyl-CoAs were affected and found no evidence to suggest this. Stearoyl-CoA desaturase (Δ9-desaturase) activity was normal when measured in microsomes from RAW.12 cells and the conversion of stearate to oleate (which requires the Δ9-desaturase system) by intact RAW.12 cells was unaltered compared to wild-type cells. The conversion of linoleate to arachidonate by intact cells (which requires the Δ5 and Δ6 desaturase activities) was also normal in the mutant cells. Fatty acid analyses showed no decreases in the relative levels of the unsaturated fatty acids that require the Δ9, Δ6 and Δ5 desaturase activities for biosyntheses of 18:1, 18:3, and 20:4 respectively. Analysis of the cytochrome b 5 cytochrome b 5 reductase ele transport system, which supports Δ1'-desaturase activity, showed only a modest (30%) decrease in activity. These data suggest that the Δl′-desaturase system contains at least one component (possibly the terminal desaturase) that is not shared by the acyl-CoA desaturases examined and that RAW.12 is deficient in this component.