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

Diamide, a thiol oxidizing agent, partially inhibited Pi uptake by rat liver mitochondria. The inhibition was temperature dependent; at 20 degrees C, the optimal temperature for maximum inhibitory effect, diamide also reduced the minimal amount of mersalyl required for the inhibition of Pi transport. Under the same conditions no inhibitory effect on Pi efflux was observed. The amount of mitochondrial thiol groups titrated by the amounts of diamide needed for the inhibition of Pi uptake was on the order of 5 nmole/mg protein. Unlike liver mitochondria, the Pi transport system of heart mitochondria was insensitive to diamide. On the contrary, accumulation of Pi 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 Pi transport system in mitochondrial membranes.