Mode of inhibition of activity of Na+-K+-stimulated adenosine triphosphatase by indomethacin.

1. The activity of the overall Na+-K+-ATPase reaction was inhibited by indomethacin in vitro. 2. The K+-NPPase activity was also inhibited by indomethacin. 3. The activity of Na+-dependent phosphorylation of Na+-K+-ATPase was activated by indomethacin. 4. Indomethacin required for 50% inhibition of K+-NPPase activity was 0.4 mM. 5. Inhibition mode of indomethacin for both the substrate and K+ in K+-NPPase reaction was competitive type. 6. The Ki values for indomethacin for the substrate and K+ in K+-NPPase reaction were 0.4 and 0.24 mM, respectively. 7. Inhibitory effect of indomethacin on K+-NPPase was reversible.