Phosphate-dependent Substrate Transport into Mitochondria

The oxidation of malate and citrate by isolated plant mitochondria can be stimulated by the addition of inorganic phosphate. This stimulation (a) is not inhibited by oligomycin or uncouplers; (b) can not be duplicated by addition of adenine nucleotide; (c) is inhibited by 2-n-butylmalonate; and (d) is not evident in detergent-treated mitochondria. Phosphate was required to elicit uncoupler-stimulated respiration. It is concluded that these effects of phosphate are attributable to a stimulated rate of substrate penetration into the mitochondria, and do not involve the oxidative phosphorylation process.Disrupting the mitochondria with detergent removed the requirement for phosphate and showed that butylmalonate did not inhibit the respiratory enzymes.