Phosphate transport in mitochondria and submitochondrial particles: The influence of thiol oxidation

Abstract

Diamide, a thiol oxidizing agent, partially inhibited P _i uptake by rat liver mitochondria. The inhibition was temperature dependent; at 20°C, the optimal temperature for maximum inhibitory effect, diamide also reduced the minimal amount of mersalyl required for the inhibition of P _i transport. Under the same conditions no inhibitory effect on P _i efflux was observed. The amount of mitochondrial thiol groups titrated by the amounts of diamide needed for the inhibition of P _i uptake was on the order of 5 nmole/mg protein. Unlike liver mitochondria, the P _i transport system of heart mitochondria was insensitive to diamide. On the contrary, accumulation of P _i into submitochondrial heart vesicles, previously loaded with MnCl₂, was inhibited by diamide. These results outline the different positional character of membrane thiol groups of mitochondria from various sources, and provide further evidence of an asymmetric orientation of the P _i transport system in mitochondrial membranes.