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Interactions of uncoupling agent and of antimycin A with cytochrome b in yeast and heart muscle preparation under anaerobic conditions

1970; Elsevier BV; Volume: 139; Issue: 2 Linguagem: Inglês

10.1016/0003-9861(70)90489-3

1096-0384

Ladislav Kováč, P. Šmigáň, E. Hrušovská, B. Hess,

Cardiovascular and exercise physiology

When added to an anaerobic suspension of aerobically grown yeast, of mitochondria isolated from it, or of Keilin-Hartree heart muscle preparation, uncoupling agents elicited a considerable oxidation of cytochrome b. For a maximum effect, about three orders of magnitude higher concentrations were required than those effective in uncoupling oxidative phosphorylation, but an extrapolation to zero of the curve relating oxidation of cytochrome b to uncoupler concentration indicates that a slight effect may also occur at uncoupling concentrations. Ubiquinone was also partly oxidized, while cytochromes a·a3 and c + c1 remained unaffected. An unknown component of mitochondria may accept electrons from cytochrome b under these conditions. The effect was rather specific for uncoupling agents and was not displayed by a number of compounds devoid of uncoupling capacity. Antimycin A added to intact yeast cells or to isolated yeast mitochondria under anaerobic conditions also induced the anaerobic oxidation of cytochrome b. Under aerobic conditions, however, antimycin A prevented the cytochrome b oxidation via the respiratory chain and caused an additional slight reduction of cytochrome b to a form whose absorption maximum in the α-region was shifted to 565 nm. In the heart muscle preparation, antimycin A did not induce cytochrome b oxidation under anaerobic conditions but did cause an additional reduction by succinate of cytochrome b to the form absorbing at 565 nm. In normal ubiquinone-containing heart muscle particles, uncoupling agents did not induce the anaerobic oxidation of that part of cytochrome b which wits reducible by succinate in the presence of antimycin A. However, in ubiquinone-depleted particles, this part of cytochrome b became accessible to the uncoupler-induced anaerobic oxidation. The antimycin A block preventing oxidation of cytochrome b by air via the respiratory chain was relieved by some uncouplers at very high concentrations.