Spectral study of b cytochromes in yeast mitochondria and intact cells |
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Authors: | Nobuhiro Sato Tomoko Ohnishi and Britton Chance |
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Institution: | Johnson Research Foundation, the School of Medicine, University of Pennsylvania, Philadelphia, Pa. 19104, U.S.A. |
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Abstract: | Three types of b cytochromes are demonstrated in Candida utilis mitochondria. One of these b cytochromes has a symmetrical -band at 561.5 nm at room temperature. This b cytochrome is readily reduced either by anaerobiosis or by cyanide treatment in the presence of glycerol 1-phosphate or succinate both in coupled and uncoupled mitochondria. The second b cytochrome has a double -band at 565 nm and 558 nm. This b cytochrome is readily reduced either by anaerobiosis or by cyanide treatment in the presence of glycerol 1-phosphate or succinate in coupled mitochondria, but in uncoupled mitochondria it is slowly reduced after anaerobiosis and this reduction rate is enhanced by antimycin A addition. Thus the oxidation-reduction state of this cytochrome is energy dependent. The first cytochrome is spectroscopically identified as cytochrome bK and the second as cytochrome bT. The third b cytochrome has an -band around 563 nm (b563) and is reduced slowly after anaerobiosis in uncoupled mitochondria but faster than the bT. Further properties of this component are not known. Midpoint potentials of cytochromes bT, b563 and bK are approximately −50 mV, +5 mV, and +65 mV, respectively.In intact cells, cytochrome bT is reduced immediately after anaerobiosis or cyanide treatment, and rapidly oxidized when uncoupler is added. Addition of antimycin A instead of uncoupler to the anaerobic cells causes oxidation of mainly cytochrome bT while addition of antimycin A to the aerobic cells results in a reduction of the cytochrome bT. |
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