CYTOCHROMES C-DEPENDENT AEROBIC RESPIRATION OF PARACOCCUS-DENITRIFICANS

Terminal parts of the respiratory chain of Paracoccus denitrificans containing cytochromes c have been investigated through the use of NNN'N'-tetramethyl-p-phenylenediamine (TMPD) as an electron donor. The cells have been shown to possess two major membrane bound TMPD oxidases characterized by their different sensitivities to cyanide. The more sensitive one, identified as cytochrome aa3, appears to be produced under oxygen-rich growth conditions, whereas a less sensitive and as yet uncharacterized enzyme accompanied with only moderate amounts of cytochrome aa3 functions when oxygen becomes limiting. The soluble periplasmic cytochrome cd1 does not contribute significantly to the total oxygen consumption rate, although its maximal catalytic capacity may be high. The fact thap the activity of alternative TMPD oxidase is not proportional to cytochrome o content is discussed in relation to possible occurrence of two distinct cytochrome o-type terminal oxidases.