(Na+ + K+)-stimulated ATPase inhibition by cesalin and macromomycin

(Na+ + K+)-stimulated ATPase was purified from dog kidney and its catalytic and glycoprotein subunits were separated. The enzymatic activity of the ATPase was totally inhibited by ouabain and partially inhibited by cesalin, maromomycin, concanavalin A, and wheat germ agglutinin. The inhibitions by cesalin or macromomycin can be reversed by the addition of phosphatidylethanolamine or phosphatidylserine, but not phosphatidylcholine. The specific binding of 125I-cesalin to the enzyme was inhibited by concanavalin A, wheat germ agglutinin, macromomycin, and the antibodies prepared in rabbits against the holoenzyme and the glycoprotein subunit, but not by ouabain, simple sugars, or the antibody against the catalytic subunit. It is proposed that the antitumor activities of cesalin and macromomycin are initiated in part by their binding to the glycoprotein subunit of (Na+ + K+)-ATPase in the plasma membrane.