A mutant of Paracoccus denitrificans with disrupted genes coding for cytochrome c550 and pseudoazurin establishes these two proteins as the in vivo electron donors to cytochrome cd1 nitrite reductase.
In Paracoccus denitrificans, electrons pass from the membrane-bound cytochrome bc(1) complex to the periplasmic nitrite reductase, cytochrome cd(1). The periplasmic protein cytochrome c(550) has often been implicated in this electron transfer, but its absence, as a consequence of mutation, has previously been shown to result in almost no attenuation in the ability of the nitrite reductase to function in intact cells. Here, the hypothesis that cytochrome c(550) and pseudoazurin are alternative electron carriers from the cytochrome bc(1) complex to the nitrite reductase was tested by construction of mutants of P. denitrificans that are deficient in either pseudoazurin or both pseudoazurin and cytochrome c(550). The latter organism, but not the former (which is almost indistinguishable in this respect from the wild type), grows poorly under anaerobic conditions with nitrate as an added electron acceptor and accumulates nitrite in the medium. Growth under aerobic conditions with either succinate or methanol as the carbon source is not significantly affected in mutants lacking either pseudoazurin or cytochrome c(550) or both these proteins. We concluded that pseudoazurin and cytochrome c(550) are the alternative electron mediator proteins between the cytochrome bc(1) complex and the cytochrome cd(1)-type nitrite reductase. We also concluded that expression of pseudoazurin is mainly controlled by the transcriptional activator FnrP.
Pearson
Isobel V
IV
Department of Biochemistry, University of Oxford, Oxford OX1 3QU, United Kingdom.
Page
M Dudley
MD
van Spanning
Rob J M
RJ
Ferguson
Stuart J
SJ
D000693:Anaerobiosis; D001400:Azurin / Q000031:analogs & derivatives* / Q000032:analysis / Q000235:genetics* / Q000378:metabolism; D001483:Base Sequence; D001692:Biological Transport; D003001:Cloning, Molecular; D003574:Cytochrome c Group / Q000032:analysis / Q000172:deficiency / Q000235:genetics* / Q000378:metabolism; D003580:Cytochromes; D004579:Electron Transport; D003576:Electron Transport Complex IV / Q000032:analysis / Q000378:metabolism*; D005798:Genes, Bacterial; D000432:Methanol; D008969:Molecular Sequence Data; D009572:Nitrite Reductases / Q000032:analysis / Q000378:metabolism*; D010231:Paracoccus denitrificans / Q000254:growth & development / Q000378:metabolism*; D016415:Sequence Alignment; D019802:Succinic Acid
D003574:Cytochrome c Group; D003580:Cytochromes; C047163:pseudoazurin; D001400:Azurin; C031732:cytochrome C-550; D019802:Succinic Acid; D009572:Nitrite Reductases; C028123:nitrite reductase (NO-forming); D003576:Electron Transport Complex IV; D000432:Methanol