The effect of phosphine on electron transport in mitochondria

Abstract

The effects of phosphine on electron transport and on some partial reactions of oxidative phosphorylation of mitochondria from mouse liver, housefly flight muscles and granary weevils has been studied. Phosphine was a strong inhibitor of respiration of mitochondria in the “active” state (state 3), uncoupled state, and ion-pumping state on glutamate, pyruvate plus malate, succinate, α-glycerophosphate, and ascorbate-cytochrome c as substrates. Respiration of mitochondria in state 3 was completely inhibited by about 250 μM phosphine. By contrast, the respiration of mitochondria in state 4 was much less sensitive. This inhibition could not be released by uncouplers suggesting that it is due to a direct effect on electron transport. Only site III was inhibited to any significant extent. Kinetic studies show that the inhibition was noncompetitive with Ki ranging from 1.6×10 −5 to 7.2×10 −5 depending on the source and purity of cytochrome oxidase. The inhibition of site III was also more pronounced in sonicated particles than in intact mitochrondria. The significance of this is discussed in relation to membrane sideness and topology of the components of the respiratory chain. Phosphine was unable to activate the “latent” ATPase nor did it have any inhibition of the Mg 2+-simulated ATPase and only high levels (1.1 m M) showed modest inhibition (41%) of uncoupler-stimulated ATPase. Phosphine had no effect on the ATP-Pi exchange and on the ATP-ADP exchange reaction at concentrations causing strong respiratory inhibition.