Variation of oleate/cis-vaccenate ratios and its regulation by substrates in hepatic tissues.

The oleate (delta 9-18:1)/cis-vaccenate (delta 11-18:1) ratios in phospholipids increased in the order of normal liver, host liver and hepatoma in rats. The amount of oleate increased in phospholipids and decreased in triacylglycerol in the same order, whereas the distributions of cis-vaccenate among the major lipid classes were relatively unchanged among the three kinds of cells. Biochemical bases for these differences were sought by characterizing the microsomal elongation system and by analyzing the elongation and desaturation products in vitro. Kinetic parameters for the elongations of palmitoyl-CoA and palmitoleoyl-CoA did not account for the observed differences in the oleate/cis-vaccenate ratios in these cells. However, the oleate/cis-vaccenate ratios varied depending on the availability of substrates, NADH, NADPH, and malonyl-CoA, in the elongation and desaturation of palmitoyl-CoA. Based on the results, it is proposed that differences in the concentrations of substrates for the elongation and desaturation systems might account at least in part for the differences in the oleate/cis-vaccenate ratios among the three kinds of cells.