Transport of phosphate analogues in rat-liver mitochondria.

The swelling of rat liver mitochondria has been studied in isotonic ammonium salts of phosphate, thiophosphate, monofluorphosphate, difluorphosphate or in isotonic ammonium malate induced by low concentrations of the mentioned anions. The data lead to the following conclusions. 1. Phosphate, thiophosphate, and monofluorphosphate are taken up by the mitochondria, whereas difluorphosphate is not, indicating that the substrate of the transporter represents the divalent anion HPO24- and not H2PO4-. 2. Thiophosphate, monofluorphosphate and phosphate, but not difluorphosphate induce the swelling of mitochondria in isotonic ammonium malate, only after a lag phase. The length of the lag phase depends on the concentration of inducing anion and pH. This phenomena cannot be explained by the current concept of two independent phosphate-transporting systems in mitochondria.