EFFECT OF HYDROGEN-PEROXIDE AND HYPOCHLORITE ON THE ACTIVITY OF NA,K-ATPASE FROM BRAIN

Brain Na,K-ATPase was subjected to the direct inhibitory effect of hyp ochlorous anion and hydrogen peroxide. The K-0.5 for the first compoun d was 20-40 mu M, for the second 1 mM. The inhibitory effect of hydrog en peroxide was partially (20-30%) prevented by deferoxamine, thus dem onstrating that in part the inhibition is connected with the generatio n of hydroxyl radicals. Carnosine, homocarnosine, and the hydrophobic antioxidants alpha-tocopherol and ionol protected Na,K-ATPase from oxi dation by H2O2, their equally effective concentrations being 10 mM for carnosine, 5 mu M for alpha-tocopherol, and 0.5 mu M for ionol. The d ata indicate that inhibition of Na,K-ATPase by oxidants is explained b y their direct effect on the protein molecule and the protecting actio n of natural hydrophilic antioxidants is connected with quenching of h ydroxyl radicals.