ATPase inhibitor and apparent deficiency of uncoupler-stimulated ATPase activity in mitochondria of houseflies ( Musca domestica L.)

Abstract

1. 1. The uncoupler- and Mg 2+-stimulated ATPase activity of thoracic muscle mitochondria of houseflies has been studied in relation to the composition of the isolation medium. 2. 2. Mitochondria isolated in isotonic sucrose solution showed a low uncoupler- and Mg 2+-stimulated ATPase activity. 3. 3. Activation of both ATPases was evident in mitochondria that were isolated in a sucrose medium supplemented with EDTA or oxidizable substrates. 4. 4. The substrate-activated response to DNP was abolished by cyanide and antimycin A. 5. 5. Mitochondria that were isolated in sucrose medium supplemented with Mg ATP show a very low Mg 2+-stimulated ATPase activity which was enhanced by substrate, EDTA and KCl. 6. 6. The Mg 2+-stimulated ATPase of fly submitochondrial particles was enhanced by trypsin. 7. 7. The activating effect of EDTA, substrates and KCl and the suppressing effect of MgATP is consistent with the fact that the former group of agents promotes a dissociation of the Pullman-Monroy type of endogenous inhibitor from the ATPase molecule while MgATP enhances the association of the inhibitor with the ATPase molecule. 8. 8. It is suggested that the inhibited ATPase complex has physiological significance in the energy needs of this muscle which is highly specialized for flight.