Regulation of respiration in paracoccus denitrificans: the dependence on redox state of cytochrome c and [ATP]/[ADP][Pi].

The respiratory rates of Paracoccus denitrificans cells, membrane fragments, and detergent-solubilized, ammonium sulfate-precipitated membrane fractions were measured with NADH and ascorbate plus N,N,N′,N′-tetramethyl-p-phenylenediamine as the substrates. It was found that the turnover numbers for cytochrome c were the same in the three preparations giving maximum values of approximately 300 s^?1 at 100% reduction of cytochrome c. NADH was rapidly oxidized in the detergent-solubilized, ammonium sulfate-precipitated membrane fraction which contained tightly bound cytochrome c. It is suggested that tight binding of cytochrome c in P. denitrificans does not impair its electron transport activity. The respiration of intact cells was dependent on the redox state of cytochrome c over a wide range of cytochrome c reduction, on the intracellular ATP]/ADP]P_i] and on the pH of the suspending medium. A conclusion is drawn that the basic principle(s) underlying regulation of cellular respiration is the same in the prokaryotic P. denitrificans and in mitochondria-containing eukaryotic organisms.