INCORPORATION OF STEARIC-ACID (18 0) AND PALMITIC ACID (16/0) IN PHOSPHOLIPID MOLECULAR-SPECIES STUDIED IN ISOLATED RAT-LIVER CELLS/

The incorporation of [1-C-14]16:0 and [1-C-14]18:0 in the molecular sp ecies of PC and PE in isolated rat liver cells was studied. More [C-14 ] 18:0 than [C-14] 16:0 was esterified both in PC and PE. Also the cha in elongated and desaturated products (16:1, 18:0 and 18:1) were incor porated. The main molecular phospholipid species formed from [C-14]18: 0 were 18:0-18:2, 18:0-20:4 and 18:0-22:6. 18:0-18:0 species was not d etected, independent of the substrate concentration (0.1-0.9 mM). With [C-14]16:0 at low substrate concentration (0.1 mM) the dominating spe cies are 16:0-18:2, 16:0-20:4 and 16:0-22:6. These species were detect ed already after 10 min. The same main species are formed both in PC a nd PE, but the relative amounts differ. In PC the combination with 18: 2 is most abundant for both saturated fatty acid substrates. In PE 18: 0-20:4 dominates when 18:0 is the substrate, and 16:0-22: 6 when 16:0 is. At higher substrate concentrations (0.4-0.9 mM) 16:0 is also ester ified in 16:0-16:0. This molecular species is efficiently degraded in the cells within 2-3 h, in contrast to the other species formed. The r esults suggest that 16:0 and 18:0 are directly incorporated in the sn- 1 position in physiologically important phospholipid molecular species . With an excess of 16:0, 16:0-16:0 is also formed in substantial amou nts, but this uncommon species is thereafter removed.