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.
Animals Biological Transport, Active