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A General Method for Detecting Nitrosamide Formation in the In Vitro Metabolism of Nitrosamines by Cytochrome P450s
Published on: September 25, 2017
Ammonia oxidation by Nitrosomonas eutropha with NO(2) as oxidant is not inhibited by acetylene
Ingo Schmidt1, Eberhard Bock2, Mike S M Jetten1
1Department of Microbiology, University of Nijmegen, Toernooidveld 1, 6525 ED Nijmegen, The Netherlands1.
Abstract:
The effect of acetylene ((14)C(2)H(2)) on aerobic and anaerobic ammonia oxidation by Nitrosomonas eutropha was investigated. Ammonia monooxygenase (AMO) was inhibited and a 27 kDa polypeptide (AmoA) was labelled during aerobic ammonia oxidation. In contrast, anaerobic, NO(2)-dependent ammonia oxidation (NO(2)/N(2)O(4) as oxidant) was not affected by acetylene. Further studies gave evidence that the inhibition as well as the labelling reaction were O(2)-dependent. Cells pretreated with acetylene under oxic conditions were unable to oxidize ammonia with O(2) as oxidant. After these cell suspensions were supplemented with gaseous NO(2), ammonia oxidation activity of about 140 micromol NH(4)(+) (g protein)(-1) h(-1) was detectable under both oxic and anoxic conditions. A significantly reduced acetylene inhibition of the ammonia oxidation activity was observed for cells incubated in the presence of NO. This suggests that NO and acetylene compete for the same binding site on AMO. On the basis of these results a new hypothetical model of ammonia oxidation by N. eutropha was developed.
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