Respiration-driven proton translocation has been studied with the oxidant pulse method for cells of denitrifying Paracoccus denitrificans oxidizing H2 during reduction of O2, NO- 3, NO- 2 or N2O. A simplified scheme of anaerobic electron transport and associated proton translocation is shown that is consistent with the measured H+ oxidant ratios. Furthermore, the kinetics and energetics of NO- 3 uptake in whole cells of P. denitrificans were studied. For this purpose, we measured H2 consumption or N2O production after addition of NO- 3 to a cell suspension, which indirectly gave information about uptake (and reduction) of NO- 3. It was found that a lag phase in H2 consumption or N2O production appeared whenever the membrane potential was dissipated by addition of thiocyanate, carbonyl cyanide m-chlorophenylhydrazone or triphenyl-methylphosphonium bromide. However, these lag phases were not observed when NO- 2 was present at the moment of introduction of NO- 3. On the basis of these findings we conclude that there are two uptake systems for NO- 3. One system is dependent on the proton-motive force and is probably used for initiation of NO- 3 uptake. The other is an NO- 3 NO- 2 antiport and its function is to take over NO- 3 uptake from the first system.
|Number of pages||13|
|Journal||Biochimica et Biophysica Acta (BBA) - Bioenergetics|
|Publication status||Published - 30 Jun 1983|
- (P. denitrificans)
- Electron transport
- Nitrate uptake
- Proton translocation