Studies on The Mechanism of Reactive Oxygen Species Inactivation of Brain Microsomal Na+-K+-ATPase

Abstract

Effects of xanthine/xanthine oxidase on the brain microsomal fraction were studied with respect to its Na+ -K+ -ATPase activity, lipid peroxidation and SH-group oxidation, The treatment of the membrane fraction with xanthine/xanthine oxidase resulted in the inactivation of Na+ -K+ -ATPase and a proportionate loss of the membrane SH-groups with sparing production of malondialdehyde. The observed amount of malondialdehyde was much less than that by another oxidizing agents, Cu + + - HzOz exhibiting the comparable degree of the ATPase inactivation, The inactivated ATPase by xanthine/xanthine oxidase was not recovered with various phospholipids. Among the quenchers, only those which prevented the inactivation of the ATPase recovered the loss of the membrane SH-groups, and the extent of SH-group recovery was correlated to that of the ATPase activity. Furthermore, SH-group-containing compounds (cysteine and glutathione) prevented the ATPase a.gainst the inactivation when the membrane fraction was treated with xanthine/xanthine oxidase in the presence of them. Serine showed no effect in this respect The results obtained suggest that reactive oxygen species inactivate brain microsomal Na + - K+ -ATPase primarily by interacting with SH-groups, which appear to be more susceptible than membrane phospholipid components to oxidative attack by the reactive oxygen species,