Cytochrome oxidase and its derivatives. VIII. Formation and properties of the ‘oxygenated’ from of cytochrome oxidase and its reconversion to ferrous and ferric oxidase
1967; Elsevier BV; Volume: 143; Issue: 3 Linguagem: Inglês
10.1016/0005-2728(67)90055-2
ISSN1879-2650
Autores Tópico(s)Mass Spectrometry Techniques and Applications
Resumo1. The ‘oxygenated’ compound of cytochrome c oxidase used in our experiments is more stable than the compound of previous reports. It is quantitatively reversible to ferrous oxidase. 2. It is best formed with an excess of O2 after reduction with a minimum amount of dithionite. It can also be formed at low O2 tension, but then contains some ferric oxidase. 3. Its formation from ferrocyanide-reduced oxidase remains incomplete and subsequent reduction by dithionite is also incomplete. 4. Cyanide does not inhibit its formation from ferrous oxidase. If only ferricytochrome a but no ferricytochrome a3 is reduced in the presence of cyanide by dithionite, there is no reaction with O2. 5. The anaerobic reduction of ‘oxygenated’ oxidase by dithionite is monophasic and fast. In contrast, that of ferric oxidase is biphasic, with an initial fast reduction of ferricytochrome a followed by a much slower reduction of ferricytochrome a3. The rate of cytochrome a, but not that of cytochrome a3 reduction depends on dithionite concentration. 6. In the presence of dissolved O2, the ferric oxidase reduction comes to a temporary standstill when one-third of the absorbance increase at 444 mμ has been reached. 7. Ethyl hydrogen peroxide reacting with ferrous oxidase forms a compound similar to the ‘oxygenated’ compound. 8. Hydrogen donors known to react with peroxidase-H2O2 complexes, particularly pyrogallol, accelerate the transformation of ‘oxygenated’ to ferric oxidase, though not at a rate comparable to that of cytochrome c. 9. These results strengthen the evidence for cytochromes a and a3 but indicate that this difference has disappeared in ‘oxygenated’ oxidase.
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