[The effect of hydrogen peroxide and hypochlorite on brain Na,K-ATPase activity]

Brain Na,K-ATPase is subjected to direct modifying influence of the hypochlorite anion and hydrogen peroxide resulting in irreversible inactivation of the enzyme. The K0.5 values for these compounds are 20-40 microM and 1 mM, respectively. The inhibiting effect of hydrogen peroxide is suppressed by desferrioxamine (by 20-30%) which indicates that the H2O2-induced inhibition is partly due to the generation of the hydroxyl radical. Carnosine, homocarnosine and the hydrophobic antioxidants, alpha-tocopherol and ionol, protect the enzyme from H2O2: their effective concentrations are to 10 mM (carnosine), 5 microM (alpha-tocopherol), and 0.5 microM (ionol). The data obtained suggest that inhibition of Na,K-ATPase by the antioxidants is caused by their direct action on the protein molecule, while the protective effect of natural hydrophilic antioxidants are due to the quenching of the hydroxyl radical.