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To elucidate the specific features of the ATP-hydrolases structural resistance in the membrane under the action of the prooxidants: Fe2' and hydrogen peroxide, and N-ethylmaleimide (NEM) the colonic smooth muscle (CSM) Na+, K(+)-ATPase activity was compared with activities of the corresponding Mg(2+)-ATP-hydrolase and ATPases from kidney medullar layer of rats. The inhibition study of the CSM Na+, K(+)-ATPase by divalent iron shows the decrease of the activity by 30% at 0.1 μM FeSO4 and in the range of 0.1-10 μM--to 45% of residual activity. When comparing with kidney enzyme (rep- resents exclusively α1-isozyme) the CSM Na+, K(+)-ATPase sensitivity to Fe2+ is reliably higher at its submicromolar concentration. CSM Mg2+-ATPase is much more resistant to iron ions effect, than kidney one. However for two tissues Mg2(+)-ATPase activity is always more resistant as compared with corresponding Na+, K(+)-ATPase activity. Against 1 mM EGTA Na+,K(+)-ATPase and Mg2(+)-ATPase activities of GMOK and kidneys are equally insensitive to effect of hydrogen peroxide in concentration up to 1 mM. But in the presence of 20 μM FeSO4 in the concentration range of 1 nM-1 mM of H2O2 the Na+, K(+)-ATPase is inhibited to greater extent, than Mg2+-ATPase activity. NEM sensitivity of the two ATP-hydrolase systems corresponds to prooxidant sensitivity that indicates the distinct importance of SH-groups for their functioning. It is concluded that Na+, K+-ATPase can serve as a marker of membrane sensitivity to oxidation, Mg(2+)-ATPase is resistant to oxidation and can be considered as criterion of the oxidation resistance when comparing membrane enzyme complexes, es- pecially in GMOK.

The influence of iron ions on ATP-hydrolases activity of cell membranes of rat colon smooth muscle and kidney