Inhibition of Succinate Ubiquinone Reductase by an Extract of Acetone Treated Mitochondria

Abstract

The properties of rat liver mitochondria treated with acetone con-taining various proportions of water were investigated. Acetone con-taining one percent of water extracted ubiquinone (UQ) quantitatively from mitochondria without causing any significant change in the con-tent of phospholipid. This preparation consumed oxygen with succinate as substrate on addition of cytochrome c alone, and UQ had little in-fluence on this activity. Thus, oxygen seemed to be consumed via a UQ independent pathway.
A phosphate buffer extract (F-S) of mitochondria which were pre-treated with acetone containing one percent water inhibited the succinate-UQ reductase activity of the insoluble residue (R). From the effects of heat, gel filtration of Sephadex, and chymotrypsin [EC 3.4.4.5] treatment, the inhibitory factor in F-S seemed to be a protein. This protein factor was not readily solubilized unless mitochondria were pre-treated with aqueous acetone. A marked inhibitory effect of F-S was observed when it was allowed to come into contact with UQ in a high ionic strength medium before incubation with R. The mechanism of inhibition of succinate-UQ reductase by F-S was discussed.