The membrane-bound b and c-type cytochromes of Proteus mirabilis grown under different conditions

Abstract

The b and c-type cytochromes present in cytoplasmic membranes of Proteus mirabilis, which had been grown under different conditions, were characterized by means of analysis of 77K spectra monitored at different oxidation-reduction potentials.

After aerobic growth as well as after anaerobic growth in the presence and absence of nitrate one or more high midpoint potential b-type cytochromes were found (E′₀ approx. 150 mV). Especially after aerobic growth the contribution of this cytochrome (these cytochromes) to the absorbance in the 535–575 nm region of 77K spectra was very large (63%). 29% could be attributed to an a-band at about 563 nm and 34% to an a-band at 556 nm. After anaerobic growth in the presence of nitrate the high potential cytochrome(s) yielded a-bands at about 561 nm (7%) and 556 nm (31%) and after anaerobic growth in the absence of a terminal electron acceptor a-bands were found at about 560 nm (26%) and 555 nm (13%).

b-Type cytochromes with midpoint potentials between 10 and 50 mV were found after both aerobic- and anaerobic growth conditions. Especially after anaerobic growth in the presence of nitrate the contribution of a cytochrome b-556 (E′₀ =24 mV) to the absorbance band between 535 and 575 nm was very large (57%). After aerobic growth the contribution of cytochrome b-557 (E′₀=49 mV) was 22%, while after anaerobic growth in the absence of a terminal electron acceptor the contribution of cytochrome b-557 (E′₀=10 mV) was only 14%.

Low potential b-type cytochromes were especially found after anaerobic growth in the absence of a terminal electron acceptor; 21% cytochrome b-556 (E′₀=-121 mV) and 19% cytochrome b-557 (E′₀=-242 mV). After aerobic growth 14% cytochrome b-556 was found with a midpoint potential of about-106 mV.

A small percentage cytochrome c (μ_m about 548–549 nm) was found in the three types of cells. Its midpoint potential was about 75 mV.