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1) The effect of 4-hydroxynonenal and lipid peroxidation on the activities of glucose-6-phosphatase and palmitoyl CoA hydrolase were studied. 2) 4-Hydroxynonenal inactivates glucose-6-phosphatase but has no effect on palmitoyl-CoA hydrolase. These effects are similar with those observed during lipid peroxidation of microsomes. 3) The inhibition of glucose-6-phosphatase by 4-hydroxynonenal can be prevented by glutathione but not by vitamin E. The inactivation of glucose-6-phosphatase during lipid peroxidation is prevented by glutathione and delayed by vitamin E. 4) The formation of 4-hydroxynonenal during lipid peroxidation was followed in relation to the inactivation of glucose-6-phosphatase. At 50% inactivation of glucose-6-phosphatase the 4-hydroxynonenal concentration was 1.5 microM. To obtain 50% inactivation of glucose-6-phosphatase by added 4-hydroxynonenal a concentration of 150 microM or 300 microM was needed with a preincubation time of 30 and 60 min, respectively. 5) It is concluded that the glucose-6-phosphatase inactivation during lipid peroxidation can be due to the formation of 4-hydroxynonenal. The formed 4-hydroxynonenal which inactivates glucose-6-phosphatase is located in the membrane. If this mechanism is valid it implies that a functional SH group of glucose-6-phosphatase is layered in the membrane. However, an inactivation of glucose-6-phosphatase by desintegration of the membrane by lipid peroxidation cannot be ruled out.

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Incubation of phosphatidylethanolamine containing liposomes with malondialdehyde and other aldehydes with different chain lengths results in the fluorescence of chromolipids. Relative to malondialdehyde, the fluorescence was greatly enhanced with increasing chain length upon incubation of 2-alkenals with phospholipids. Similar results were found using the total lipid extracted from erythrocyte ghosts. It seems that the hydrophobic character of the aldehydes is important for the amount of fluorescence detected in lipid bilayers.

SUMMARYr.Atdifferent timeintervals afterinjectionof [r(3)-SH]glycerol, theincorporation of glycerol into the various molecular species of phosphatidylcholine and phosphatidylethanolamine from rat liver, and phosphatidylcholine from rat lung was determined.2. The results indicate that, in liver, a de rtovo synthesis is primarily operating in the biosynthesis of linoleic acid-containing molecules of lecithin and of the hexaenoic molecular species of phosphatidylethanolamine. An acylation of monoacyl derivatives of these phospholipids is suggested to play an important role particularly in the formation of arachidonic acid containing molecular species of these phospholipids.3. In lung, the de MOVO synthesis was found to contribute also primarily to the linoleic acid-containing lecithins, though it also represents an important pathway for the synthesis of tetraenoic, monoenoic and, perhaps to a lesser extent, disaturated lecithins. A deacylation-reacylation mechanism may contribute significantly to the formation of dipalmitoyl lecithin, a major constituent of lung pulmonary surfactant.4. Acylation of I-palmitoyl-sn-glycero-3-phosphorylcholine with various labeled fatty acids or acyl-CoA esters was studied in the presence of microsomes from rat lung and liver. In the presence of microsomes from lung a significant uptake of palmitic acid was observed into the z-position of lecithin, this in strong contrast to the findings with liver microsomes where only a very limited uptake of palmitic acid was observed. The results endorse the findings from the in vivo studies that the acylation of monoacyl-sn-glycero-3-phosphorylcholine may play an important additional role in maintaining the high level of dipalmitoyl lecithin in lung.5. Comparison of the composition of phosphatidylethanolamine and lecithin from lung suggested, in support of previous observations by other investigators, that the methylation of phosphatidylethanolamine does not represent an important pathway for the formation of dipalmitoyl lecithin.