THE CONDENSING EFFECTS OF EGG LECITHIN AND CHOLESTEROL ON TRIOLEIN MONOLAYERS ARE INHIBITED BY SUBSTITUTION OF ONE SATURATED ACYL-CHAIN IN THE TRIACYLGLYCEROL

Previous work showed that the clearance from plasma of chylomicron-lik e emulsions injected intravenously was affected,by the acyl chains of the constituent triacylglycerols. Compared with emulsions containing t riolein (OOO) as the only triacylglycerol, clearances were decreased b y a single saturated chain in emulsions containing 1,3-dioleoyl-2-stea royl-sn-glycerol (OSO), 1,2-dioleoyl-3-stearoyl-sn-glycerol (OOS) or 1 -stearoyl-2,3-dioleoyl-sn-glycerol (SOO). The differences in clearance may reflect physical differences at the oil-water interface related t o chain interactions of the triacylglycerol structures with other lipi d components. In the present work lipid monomolecular films at the air -water interface were used to establish the capacity of OOO to interac t with the pure synthetic triacylglycerols OOS and SOO, and the capaci ty of OOS and SOO to eo-exist in monolayers of lecithin and of cholest erol was compared with OOO. Substituting one oleoyl chain by a stearoy l chain induced a 20% condensation in monomolecular films of the pure triacylglycerols. Mixtures of OOO with either pure egg yolk phosphatid ylcholine or cholesterol also showed substantial condensing effects. I n contrast substituting one oleoyl chain by a stearoyl chain substanti ally lessened the condensing effects. At surface pressures above the c ollapse pressure of the pure triacylglycerols, substantially more OOO than OOS or SOO was retained in mixed monolayers with phosphatidylchol ine. These differences could underlie the effects on metabolism of sat urated chains in emulsion triacylglycerols.