Escherichia coli can produce several respiratory chains which transfer electrons to oxygen, nitrate or other acceptors. Cytochromes are amongst the electron carriers of these chains, and can be studied by a number of spectroscopic techniques. Of particular interest is the formate-nitrate reductase respiratory pathway which is composed of two complexes, formate dehydrogenase and nitrate reductase each with a cytochrome associated.
The cytochromes of E. coli after growth under a variety of
conditions have been studied by spectrophotometry redox titration and
other spectroscopic methods. These have shown that, contrary to some
previous reports, there are at least six cytochromes produced
irrespective of the culture conditions used. This emphasizes the need
for simplified systems and two of these have been investigated. By
fractionation of cytochromes prior to spectroscopic analysis a
cytochrome b of redox potential OmV was identified in cells grown 556
aerobically. In addition the association of two cytochromes of potential +20mV and +120mV with nitrate reductase was demonstrated. Secondly the formate-nitrate reductase pathway has been investigated by spectroscopic studies of chi mutants which are defective in this activity. Three phenotypes of cytochrome production were observed. Mutants at loci associated with the production of the cofactor for both nitrate reductase and formate dehydrogenase were shown to produce the same cytochromes as the wild-type. Mutants mapping at the chlC locus and defective in nitrate reductase but not formate dehydrogenase were found to lack only the two cytochromes associated with nitrate
reductase. They had high leyels of a cytochrome of redox potential -100mV which was shown to be associated with formate dehydrogenase. A third class of pleiotropic regulatory mutants was identified which was not related with a specific genotype. These produced none of the anaerobic respiratory pathways but overproduced the aerobic respiratory pathway leading to cytochrome d. The second aerobic respiratory pathway leading to cytochrome o was most evident in double mutants lacking both of the cytochromes associated with nitrate reductase and that associated with formate dehydrogenase. On the basis of these results a model for the arrangement of the cytochromes in the respiratory chains of E. coli is proposed. / Medicine, Faculty of / Biochemistry and Molecular Biology, Department of / Graduate
| Identifer | oai:union.ndltd.org:UBC/oai:circle.library.ubc.ca:2429/23458 |
| Date | January 1982 |
| Creators | Hackett, Neil Robert |
| Source Sets | University of British Columbia |
| Language | English |
| Detected Language | English |
| Type | Text, Thesis/Dissertation |
| Rights | For non-commercial purposes only, such as research, private study and education. Additional conditions apply, see Terms of Use https://open.library.ubc.ca/terms_of_use. |
Page generated in 0.0019 seconds