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

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 delta 1'-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 (delta 9-desaturase) activity was normal when measured in microsomes from RAW.12 cells and the conversion of stearate to oleate (which requires the delta 9-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 delta 5 and delta 6 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 delta 9, delta 6 and delta 5 desaturase activities for biosyntheses of 18:1, 18:3, and 20:4 respectively. Analysis of the cytochrome b5/cytochrome b5 reductase electron transport system, which supports delta 1'-desaturase activity, showed only a modest (30%) decrease in activity. These data suggest that the delta 1'-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.