The effects of the lipid-peroxidation product 4-hydroxynonenal on the formation of fluorescent chromolipids from microsomes, mitochondria and phospholipids were studied. Incubation of freshly prepared rat liver microsomes or mitochondria with 4-hydroxynonenal results in a slow formation of a fluorophore with an excitation maximum at 360 nm and an emission maximum at 430 nm. The rate and extent of the development of the 430 nm fluorescence can be significantly enhanced by ADP-iron (Fe3+). With microsomes, yet not with mitochondria. NADPH has a catalytic effect similar to that of ADP-iron. Fluorescent chromolipids with maximum excitation and emission at 360/430 nm are also formed during the NADPH-linked ADP-iron-stimulated lipid peroxidation. Phosphatidylethanolamine and phosphatidylserine react with 4-hydroxynonenal revealing a fluorophore with the same spectral characteristics as that obtained in the microsomal and mitochondrial system. The findings suggest that the fluorescent chromolipids formed by lipid peroxidation are not derived from malonaldehyde, but are formed from 4-hydroxynonenal or similar reactive aldehydes via a NADPH and/or ADP-iron-catalysed reaction with phosphatidylethanolamine and phosphatidylserine contained in the membrane.

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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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In the process of lipid peroxidation of microsomes induced either by oxygen radicals generated by xanthine oxidase or by NADPH, ferritin is able to donate the necessary iron. The amount of ferritin necessary to catalyze the process of lipid peroxidation is in the physiological range. In contrast to the finding with phospholipid liposomes, catalase hardly stimulates the lipid peroxidation of microsomes. FerritinIron Lipidperoxidation Microsome