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.

Enzymes of oxygen metabolism and lipid peroxidation on erythrocytes from copper-deficient rats.

1. Copper deficiency in the rat results in a high decrease of erythrocyte superoxide dismutase activity (by 70%), an increase of glutathione peroxidase activity (by 17%) and glucose 6-phosphate dehydrogenase activity (by 40%) and no change in catalase activity. 2. Ascorbate (30 nM) and copper (10 and 50 nmol/mg protein) enhance about 2-fold the lipid peroxidation of erythrocyte membranes from copper-deficient rats. 3. The osmotic stability of copper-deficient rat erythrocytes is higher compared with that of the controls.