Influence de l'éthacrynate de sodium sur quelques réactions liées au mécanisme des oxydations phosphorylantes

Abstract

Influence of sodium ethacrynate on some reactions involved in the mechanism of oxidative phosphorylation 1. 1. The effects of ethacrynate on the oxidation of several substrates, on the reversal of electron transfer and on different types of ATPase are described. 2. 2. In phosphate medium, addition of ADP or 2,4-dinitrophenol strongly increases the inhibition of β-hydroxybutyrate oxidation; under these conditions, succinate oxidation is poorly inhibited (20 %). 3. 3. In a non-phosphate medium, ethacrynate strongly inhibits succinate oxidation (80 %); this inhibition is dependent on the coupling state and the level of reduced pyridine nucleotides of the mitochondria. Phosphate and ethacrynate are competitive, and bovine serum albumin counteracts the inhibition by ethacrynate. After mitochondria preincubated with ethacrynate and succinate have been washed, the inhibition of succinate oxidation is still very substantial. 4. 4. Arsenate-stimulated succinate oxidation is also strongly inhibited by ethacrynate; preincubation of arsenate with ethacrynate decreases the inhibition. 5. 5. Reversal of electron transfer is strongly inhibited by ethacrynate, energy being supplied either directly by mitochondrial oxidation, or indirectly by adding ATP under anaerobic conditions. 6. 6. Ethacrynate inhibits 2,4-dinitrophenol-stimulated ATPase and does not inhibit Mg 2+-stimulated ATPase; ATPase from frozen-thawed mitochondria is inhibited by ethacrynate only if these mitochondria have been washed after the freezing-thawing treatment.