Electron transport-linked proton translocation at nitrite reduction inCampylobacter sputorum subspeciesbubulus |
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Authors: | Wytske de Vries H G D Niekus Hugerien van Berchum A H Stouthamer |
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Institution: | (1) Biological Laboratory, Free University, De Boelelaan 1087, 1007 MC Amsterdam, The Netherlands;(2) Present address: Department of Genetics, Delft, The Netherlands |
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Abstract: | Campylobacter sputorum subspeciesbubulus contains a membrane-bound nitrite reductase which catalyses the six-electron reduction of nitrite to ammonia. Formate andL-lactate are used as hydrogen donors. Cells ofC. sputorum grown with nitrate or nitrite contain cytochromes of theb-andc-type and a carbon monoxide-binding cytochromec. In addition, a special membrane-bound carbon monoxide-binding pigment is found. Nitrite reduction with formate orL-lactate as a hydrogen donor is strongly inhibited by 2-n-heptyl-4-hydroxyquinoline-N-oxide (HQNO). Nitrite reduction by bacterial suspensions with lactate as a hydrogen donor is strongly inhibited by carbonylcyanide-m-chlorophenyl-hydrazone (CCCP) whereas nitrite reduction with formate as a hydrogen donor is not inhibited at all. H+/O values and H+/NO
2
-
values were measured with ascorbate + N,N,N ,N -tetramethyl-p-phenylenediamine (TMPD), formate (in the absence and presence of carbonic anhydrase) andL-lactate as a hydrogen donor. The results are summarized in a scheme for electron transport from formate or lactate to oxygen or nitrite which shows a periplasmic orientation of formate dehydrogenase and nitrite reductase and a cytoplasmic orientation of lactate dehydrogenase and oxygen reduction, and which shows proton translocation with a H+/2e value of 2.0. The H+/O and H+/NO
2
-
values predicted by this scheme are in good agreement with the experimental values.Abbreviations CCCP
carbonylcyanide-m-chlorophenylhydrazone
- HQNO
2-n-heptyl-4-hydroxyquinoline-N-oxide
- MTPP+
methyltriphenylphosphonium cation
- TMPD
N,N,N ,N -tetramethyl-p-phenylenediamine; H+/O ( H+/NO
2
-
), number of protons liberated in the outer bulk phase at the reduction of one atom O (one ion NO
2
-
); H+/2e ( q+/2e), number of protons (charges) translocated across the cytoplasmic membrane during flow of two electrons to an acceptor |
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Keywords: | Campylobacter sputorum subspeciesbubulus Nitrite reduction Proton translocation Localization |
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