Cytochromes of the trimethylamine N-oxide anaerobic respiratory pathway of Escherichia coli.

Escherichia coli grown anaerobically with trimethylamine N-oxide (TMAO) as a terminal electron acceptor develops a new cytochrome pathway in addition to the aerobic respiratory pathways which are still formed. Formate, NADH, and possibly other substrates derived from glucose, supply electrons to this pathway. Cytochromes with alpha-absorption peaks at about 548, 552, 554 and 557 nm are rapidly reoxidized by TMAO in a reaction which is not inhibited by 2-n-heptyl -4-hydroxyquinone N-oxide. CuSO4 inhibits the reoxidation by TMAO of the first two of these cytochromes. This suggests that the pathway of electron transfer leading to the reduction of TMAO is: substrates leads to cytochromes 548,552 leads to cytochromes 554,557 leads to trimethylamine-N-oxide reductase leads to TMAO. These cytochromes, but not those of the aerobic respiratory pathways, are reoxidized by the membrane-impermeant oxidant ammonium persulfate in intact cells. This suggests that the cytochromes of the TMAO reduction pathway and/or trimethylamine-N-oxide reductase are situated at the periplasmic surface of the cytoplasmic membrane of E. coli.