The effect of DDT and related insecticides on the mitochondrial ATPase of houseflies.

1. DDT is a weak inhibitor of the ATPase of housefly muscle mitochondria in the absence of Mg2+ but an activator in the presence of Mg2+. 2. By contrast, DDT and several p,p'-substituted alpha-trichlomethylbenzylanilines were strong inhibitors of the ATPase activity in the presence of the uncoupler, dinitrophenol. 3. Maximum inhibition of the DNP-ATPase was achieved when the ATPase complex was dissociated from its endogenous protein inhibitor. 4. The inhibition by DDT was noncompetitive, maximum at acid pH and independent of temperature. The inhibition was counteracted by exogenous phosphatidylcholine and phosphatidylethanolamine. 5. The ATPase was also activated by NH+4 in the presence of valinomycin. This activation was reversed by K+ and strongly inhibited by DDT. 6. The possible mechanisms involved in the inhibition by DDT are discussed.