The effect of ATP on the EPR spectrum of phosphorylating sub-mitochondrial particles

Abstract

1. The addition of either ATP or antimycin to substrate-reduced phosphorylating sub-mitochondrial particles causes a decline in the intensity of the EPR signals derived from free radicals and the iron-sulphur paramagnetic signals. 2. It is suggested that antimycin induces a conformation change, resulting in the redistribution of electrons within the paramagnetic centre. 3. It is suggested that ATP, on the other hand, causes the oxidation of iron-sulphur proteins. Two species are involved, one with g z = 2.02, g y = 1.94 and g x = 1.92, and one with g ⊥ = 1.94 and a g  of low intensity. With NADH as substrate, the main effect of ATP is to cause oxidation of the latter species; with succinate (in the presence of rotenone) the main effect is on the former species. 4. In the presence of antimycin, with NADH as substrate, ATP causes the oxidation of both species. With succinate as substrate (in the presence of rotenone) ATP has a much smaller effect on the g = 1.94 line in the presence of antimycin than in its absence. 5. In the presence of antimycin (but not in its absence) the addition of ATP causes the appearance of the g = 6 signal, characteristic of a 3 in partially reduced cytochrome aa 3, as well as the g ⊥ line of Cu(II). It is concluded that, when reversal of the chain is inhibited by antimycin, ATP induces a displacement of electrons within the cytochrome c oxidase molecule that results in a 3 being more oxidized than a. 6. It is pointed out that, despite the fact that 15 or 16 electron carriers have been identified in the respiratory chain, there still remain unidentified electron sinks where electrons disappear on adding ATP and reappear on adding uncoupler.