Energetic aspects of growth of Paracoccus denitrificans: oxygen-limitation and shift from anaerobic nitrate-limination to aerobic succinate-limitation - Evidence for a new alternative oxidase, cytochrome a₁

1. Growth yields and efficiency of energy conservation were the same for aerobic succinate-limited and oxygen-limited cells of Paracoccus denitrificans. 2. A shift from anaerobic nitrate-limitation to aerobic succinatelimitation showed that before and after the shift cells grew with the same capacity of energy conservation. 3. Respiration-driven proton translocation showed the presence of H⁺-translocating sites 1 and 2, which translocate respectively 2-3 and 4 protons per 2 electrons in oxygen-, anaerobic nitrate-and aerobic succinate-limited cells. 4. Cytochrome spectra and flash-photolysis spectra of oxygen- and nitrate-limited cells gave evidence for the presence of an alternative oxidase, cytochrome a₁, never before recognized in Paracoccus denitrificans. 5. Only a-type cytochromes liganded with CO could be flash-photolysed. No evidence for a functional cytochrome o was found in photolysis experiments. 6. Fast oxidation, before photolysis, of the bc-pool after introduction of oxygen in a CO-liganded sample at-20° to-30° C, indicated the presence of a cytochrome oxidase other than cytochrome a₁ with a very high affinity for oxygen and a low affinity for CO. 7. In photochemical action spectra, light released CO-inhibition of respiration, but the release was independent of the wavelength used (560-610 nm).