Characterization and phenotypic control of the cytochrome content of Escherichia coli

TLDR: Redox titrations performed in the presence of CO showed that one of the b-type cytochromes in the aerobically grown cultures was reduced, even at the upper limits of the range of electrode potentials (above +400mV).

Abstract: 1. Electron-transport particles derived from Escherichia coli grown aerobically contain three b-type cytochromes with mid-point oxidation–reduction potentials at pH7 of +260mV, +80mV and −50mV, with n=1 for each. The variation of these values with pH was determined. 2. E. coli develops a different set of b-type cytochromes when grown anaerobically on glycerol with fumarate or nitrate as terminal electron acceptor. Electron-transport particles of fumarate-grown cells contain b-type cytochromes with mid-point potentials at pH7 of +140mV and +250mV (n=1). These two cytochromes are also present in cells grown with nitrate as terminal acceptor, where an additional cytochrome b with a mid-point potential of +10mV (n=1) is developed. 3. The wavelengths of the α-absorption-band maxima of the b-type cytochromes at 77K were: (a) for aerobically grown cells, cytochrome b (Em7 +260mV), 556nm and 563nm, cytochrome b (Em7 +80mV), 556nm and cytochrome b (Em7−50mV), 558nm; (b) for anaerobically grown cells, cytochrome b (Em7 +250mV), 558nm, cytochrome b (Em7 +40mV), 555nm and cytochrome b (Em7 +10mV), 556nm. 4. Cytochrome d was found to have a mid-point potential at pH7 of +280mV (n=1). 5. Cytochrome a1 was resolved as two components of equal magnitude with mid-point potentials of +260mV and +160mV (n=1). 6. Redox titrations performed in the presence of CO showed that one of the b-type cytochromes in the aerobically grown cultures was reduced, even at the upper limits of our range of electrode potentials (above +400mV). Cytochrome d was also not oxidizable in the presence of CO. Neither of the cytochromes a1 was affected by the presence of CO.