Effect of chronic copper loading on the activity of rat liver antioxidative enzymes.

The activity of antioxidative enzymes SOD, catalase, glutathione peroxidase and the related glutathione reductase, glucose-6-phosphate dehydrogenase and NADPH-isocitrate dehydrogenase was examined in liver cytosol and large granule fraction (mitochondria) from control and copper-loaded rats. An increase of SOD activity (more than 100%) and a decrease of both catalase (by 60%) and glutathione peroxidase activity (by 30%) in large granule fraction were observed after copper loading. The cytosolic glutathione peroxidase activity was also markedly decreased: glutathione peroxidase I (EC 1.11.1.9)--by 35% and glutathione peroxidase II (EC 2.5.1.18)--by 75%. Cytosolic catalase activity and the glutathione reductase, glucose-6-phosphate dehydrogenase and NADPH-isocitrate dehydrogenase activities in cytosol and in mitochondria of copper-loaded rats were unchanged. It is concluded that under chronic copper loading the primary mechanisms of copper toxicity are accompanied by disturbances of the antioxidative enzyme function.

Inhibition of phospholipid hydrolysis by soluble phospholipase A2 in biological membranes of different origin after lipid peroxidation.

In peroxidized rat liver microsomal membranes phospholipid hydrolysis catalyzed by porcine pancreas phospholipase A2 was found to be inhibited. The extent of inhibition depended on the amount of lipid peroxidation products (MDA) accumulated in the membrane. This effect was not due to the direct action of lipid peroxidation products on the enzyme but to membrane modification. The same inhibitory effect was also found with other membranes--rabbit skeletal muscle sarcoplasmic reticulum, bovine retina rod outer segments and rat brain synaptosomes--differing in phospholipid and fatty acid composition. The inhibition of phospholipase reaction by lipid peroxidation depended at least on three factors: decrease in the amount of phosphatidylethanolamine; decrease in the level of phospholipids, containing polyunsaturated fatty acid residues and occurrence of membrane structural rearrangements resulting in unavailability of phospholipid substrates for phospholipase A2 attack. Membrane destruction with anionic detergent--sodium cholate--led to a sharp increase of phospholipase hydrolysis rate.

The influence of starvation on some characteristics of the Ca2+ transport system and lipid content in rat liver mitochondria.

The effects of 48-hour starvation on some characteristics of the Ca2+ transport system as well as on lipid content and free fatty acids composition in rat liver mitochondria were determined. The ion fluxes in mitochondria in steady state and oscillations were measured using Ca2+, Sr2+ and H+ sensitive electrodes. The Ca2+ uptake in liver mitochondria was changed after starvation. In the case of equal amounts of endogenous mitochondrial Ca2+ the capability of liver mitochondria to accumulate and store exogenous Ca2+ was decreased after starvation. After inhibition of the energy dependent (active) Ca2+ transport by ruthenium-red (RR) the rate of the passive Ca2+ efflux was activated and this could be explained by the induction of the electroneutral 2H+/Me2+ exchange after starvation. The disproportion in the amounts of linoleic and docosahexaenoic acids in mitochondrial phospholipids after starvation is considered to be the possible cause of the changes in the structure and permeability of the mitochondrial membrane.

[Inhibition of phospholipid hydrolysis by phospholipase A2 in microsomal and mitochondrial membranes subjected to lipid peroxidation]. / Ingibirovanie gidroliza fosfolipidov fosfolipaznoi A2 v membranakh mikrosom i mitokhondrii, podvergshikhsia perekisnomu okisleniiu lipidov.

The rate of phospholipid hydrolysis in rat liver microsomal and mitochondrial membranes catalyzed by phospholipase A2 was shown to decrease after ascorbate + Fe2+-induced lipid peroxidation. The degree of inhibition was linearly dependent on the amount of lipid peroxidation products (malonyl dialdehyde) accumulated in the membrane. The decreased phospholipid hydrolysis rate in membranes after lipid peroxidation was registered using phospholipases A2 from two sources: porcine pancreas and bee venom. It was established that the inhibitory action of phospholipid peroxidation products was not linked with a direct effect on the enzyme and was not caused by depletion of phospholipase reaction substrates (as a result of lipid peroxidation). A possible role of lateral separation of oxidized and non-oxidized lipid phases in the mechanisms of inhibition of phospholipid hydrolysis by phospholipase A2 is discussed.

Copper deficiency-induced changes in the fatty acid composition of mitochondrial and microsomal membranes of rat liver.

The effects of copper deficiency on the fatty acid composition of mitochondrial and microsomal phospholipids in rat liver were studied. Copper deficiency was induced by a milk powder diet. To evaluate the effect of the milk diet on the fatty acid pattern of mitochondrial and microsomal phospholipids, one group of rats was fed Cusupplemented powdered milk. A decrease in the relative proportion of linoleic acid and an increase in the level of oleic and docosahexaenoic acids in membrane phospholipids were found in this group. However, no changes in the fatty acid pattern characteristic of essential fatty acid deficiency were observed. Dietary copper deficiency produced a significant decrease in the relative amounts of linoleic and arachidonic acids, as well as an increase in the docosahexaenoic acid content in both mitochondrial and microsomal membranes compared to the nondeficient controls. The disproportionate quantities of polyunsaturated fatty acids are discussed with a view to the disturbances of membrane function in copper deficiency.