The low-temperature spectral properties of mammalian cytochrome oxidase. II. The enzyme isolated from beef-heart mitochondria

Abstract

A series of low-temperature spectra of isolated cytochrome oxidase are presented. 1. 1. A technique for the selective reduction of cytochrome a with dithionite is given. 2. 2. The reduced minus oxidized difference spectrum of cytochrome a shows a 601 mμ α-peak and a split Soret band with maxima at 447 and 442 mμ for ferrous a and a Soret absorption band at 426 mμ for ferric a. 3. 3. The cytochrome a 3 difference spectrum is quite different. Its ferrous α-peak is found at 604 mμ and its Soret band has a single maximum at 444 mμ. The ferric γ-band is at 412 mμ. 4. 4. Sulfide, like cyanide, was found to react with ferricytochrome a 3. 5. 5. Azide was found to react with ferrocytochrome a. The 601 mμ peak of ferrous a was shifted to 597 mμ and the split Soret band to 447 and 440 mμ. 6. 6. Under anaerobic conditions the azide effect was reversed, indicating that ferrocytochrome a can exist in two forms differing in reactivity toward azide. The form which reacts with azide is labile and in the absence of active turnover is converted to the form which does not react with azide. 7. 7. ‘Oxygenated’ cytochrome oxidase showed no Soret band splitting at low temperature.