Influence of the energetic state of rat liver mitochondria on the sensitivity of the phosphate carrier towards SH reagents.

Phosphate transport into rat liver mitochondria was measured by the swelling technique in 0.1 M ammonium phosphate. Energized or non-energized mitochondria were preincubated with different thiol reagents and evidence is given that with a slow-reacting thiol reagent, ethacrynate, the inactivation of the phosphate carrier is obtained when mitochondria are energized, while poor or no inactivation occurs when mitochondria are non-energized or preincubated with Pi. Moreover, the inactivation depends on the presence of Mg2+ and on the nature of the substrate. Some comparative essays were done using N-ethylmaleimide as a thiol reagent, but no energy-linked variation of N-ethylmaleimide inhibition on phosphate transport was obtained. Taking into account the fact that both thiol-reagents incorporation into rat liver mitochondria is sitmulated by the presence of substrate, the different behaviour of these two thiol-reagents towards Pi transport is discussed on the basis of their different reactivity with SH groups.