Effects of lipid peroxidation on membrane-bound enzymes of the endoplasmic reticulum

Abstract

1. Induction of the formation of lipid peroxide in suspensions of liver microsomal preparations by incubation with ascorbate or NADPH, or by treatment with ionizing radiation, leads to a marked decrease of the activity of glucose 6-phosphatase. 2. The effect of peroxidation can be imitated by treating microsomal suspensions with detergents such as deoxycholate or with phospholipases. 3. The substrate, glucose 6-phosphate, protects the glucose 6-phosphatase activity of microsomal preparations against peroxidation or detergents. 4. The loss of glucose 6-phosphatase activity is not due to the formation of hydroperoxide or formation of malonaldehyde or other breakdown products of peroxidation, all of which are not toxic to the enzyme. 5. All experiments lead to the conclusion that the loss of activity of glucose 6-phosphatase resulting from peroxidation is a consequence of loss of membrane structure essential for the activity of the enzyme. 6. In addition to glucose 6-phosphatase, oxidative demethylation of aminopyrine or p-chloro-N-methylaniline, hydroxylation of aniline, NADPH oxidation and menadione-dependent NADPH oxidation are also strongly inhibited by peroxidation. However, another group of enzymes separated with the microsomal fraction, including NAD(+)/NADP(+) glycohydrolase, adenosine triphosphatase, esterase and NADH-cytochrome c reductase are not inactivated by peroxidation. This group is not readily inactivated by treatment with detergents. 7. Lipid peroxidation, by controlling membrane integrity, may exert a regulating effect on the oxidative metabolism and carbohydrate metabolism of the endoplasmic reticulum in vivo.

Damage to ram spermatozoa by peroxidation of endogenous phospholipids

“…In view of reports in the literature that certain proteins and enzymes are destroyed or inactivated as a result of direct contact with lipid peroxides (Wills, 1961(Wills, ,1971, we also explored the possibility that the endogenously produced peroxides themselves exert a direct inhibitory action on the enzymes which are listed in Table 1. For this purpose we used a suspension of freshly washed spermatozoa which was sonicated for 60 sec and centrifuged at 5000 g for 15 min.…”

“…Our previous studies have shown that the formation of peroxides in spermatozoa is accompanied by loss of phospholipid from the membrane and a rapid decline in motility (Jones & Mann, 1973,1976 (Mann, 1964) Brown (1975), and /?-7V-acetylglucosaminidase by the procedure of Conchie, Findlay & Levvy (1959).…”

“…The wide¬ spread distribution of unsaturated lipids in cell membranes, and their lability in the presence of oxygen, have prompted numerous investigations into the deleterious effects of lipid peroxidation. Haemolysis of erythrocytes (Tsen & Collier, 1960), swelling of mitochondria (Hunter, Gebicki, Hoffstein, Weinstein & Scott, 1963 ;McKnight & Hunter, 1966), structural damage to DNA (Reiss & Tappel, 1973), loss of membrane integrity, and inactivation of enzymes (Roubal & Tappel, 1966;Wills, 1971) have all been ascribed to or correlated with the formation of lipid peroxides.…”

Studies of Microsomal Glucose-6-Phosphatase on Liver of Irradiated Rats

“…Hence an alteration of lipid metabo lism could have brought on enzymatic changes. Lipid peroxidation on membranes is a wellknown effect of the cellular influence of radia tion (19). It has been observed that the increase of peroxidation is connected with biochemical alterations resulting from a structural mem brane injury (2,5,10,19).…”

“…Lipid peroxidation on membranes is a wellknown effect of the cellular influence of radia tion (19). It has been observed that the increase of peroxidation is connected with biochemical alterations resulting from a structural mem brane injury (2,5,10,19). It is known that cysteamine is rapidly concentrated in the liver, and mainly on the membranes of mitochondria and endoplasmic reticulum (1).…”