Insights into the Mechanism of Na+,K+-ATPase Inhibition by 2-methoxy-3,8,9-trihydroxy Coumestan

The molecular mechanisms involved in Na+,K+-ATPase inhibition by 2-methoxy-3,8,9-trihydroxy coumestan were investigated. We show that this compound decreases the free sulfydryl groups present in the enzyme and that its inhibitory effect is prevented by dithiothreitol and other two sulfydryl containing reagents. We propose a redox cycle culminating with the irreversible oxidation of sulfydryl groups essential for the catalytic activity of this enzyme and of two other related P-type ATPases.