Proton translation in submitochondrial vesicles

An investigation of proton translocation in submitochondrial vesicles from rat liver has been made under simple experimental conditions. Choline chloride was used both as the oxidizable substrate and the ionic medium for the measurement of activity during oxygen pulse experiments:

1. The passive permeability measured from the decay of proton efflux after an oxygen pulse could be described by a first-order equation. An H⁺/O ratio of 2·5 was obtained for choline oxidation in the presence of oligomycin and/or MgCl₂. Oligomycin decreased the passive proton permeability and respiration, concomitant with an increase in proton uptake. Respiratory control was directly related to the passive proton permeability and inversely related to the magnitude of the proton gradient. The decreased respiration and passive permeability reflecting respiratory control is most evident in the pH rang 5·8–7·5.
2. Preparation of submitochondrial vesicles in the presence of EDTA resulted in proton production during an oxygen pulse given at alkaline pH. Cytochromec enhanced proton uptake by approximately 1 H⁺/cytochromec, but only in the presence of Triton X-100. These results are indicative of the asymmetric behavior of the coupling membrane and provide direct evidence of the participation of electron transport components in proton translocation.