Respiratory Control and the Proton Electrochemical Gradient in Mitochondria

The relationship between the rate of electron transport and the proton electrochemical gradient Δ H across the inner membranes of rat liver mitochondria was investigated. Δ H was calculated from ΔPH as measured by 14C‐labeled 5,5‐dimethyl‐2, 4‐oxazolidine dione distribution and from Δφ as measured by 42K distribution (in the presence of valinomycin). When mitochondria are in state 3, i.e. during phosphorylation, Δ H was only 5 m V less than in state 4, while respiration increased 3.5‐fold. In the presence of uncoupler, respiration was the same as in state 3, but Δ H was reduced by 22 m V with dinitrophenol, 28 m V with KCI + valinomycin and 60 m V with gramicidin. In the presence of valinomycin, when uncoupling increases by increasing KCl concentration, there was a linear relationship between Δ H and the rate of respiration. These results are in agreement with the suggestion that in uncoupled systems the respiratory rate is controlled by Δ H. However, the phosphorylation reaction controls the respiratory rate directly and not through its effect on Δ H. This conclusion is not compatible with the chemiosmotic model of oxidative phosphorylation.