GOSSYPOL INHIBITION OF KIDNEY （Na++K+）-ATPase

The inhibitory effect of gossypol acetic acid on the activity of (Na++K+)-ATPase partially purified from the outer medulla of rabbit kidney was examined, the IC50 is 6.5 μM. The enzyme kinetic studies show that gossypol is noncompetitive with ATP, Mg2+, Na+ and K+ with apparent Ki of 15, 13, 14.0 and 4.4 μM respectively. These data suggest that gossypol inhibition of (Na++K+)-ATPase is due to direct catalytic action at the subunit level, it may prevent proper positioning of the catalytic center or decrease the amount of active enzyme.