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Competitive inhibition of ammonia oxidation in Nitrosomonas europaea by methane, carbon monoxide or methanol
Author(s) -
Suzuki Isamu,
Kwok Siu-Chun,
Dular Usha
Publication year - 1976
Publication title -
febs letters
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.593
H-Index - 257
eISSN - 1873-3468
pISSN - 0014-5793
DOI - 10.1016/0014-5793(76)80825-3
Subject(s) - library science , nitrosomonas europaea , chemistry , computer science , organic chemistry , nitrite , nitrate
Ammonia oxidation by Nitrosomonas europaea and methane oxidation by methane-utilizing bacteria seem to have a striking similarity as pointed out by the workers of the latter organisms [ 1,2] . Both oxidations presumably start with hydroxylation of the substrates: NHs-_, NHzOH* (NOH)+NO, [3] and CI& f CHsOH+HCHO ----+ HCOOH -+COz [I] and are sensitive to similar inhibitors [ 1,4] . In addition the oxidation of methane is competitively inhibited by ammonia [ 1,2]. Although ammonia-oxidizing cell-free systems have been successfully prepared [ 5,6] , it has been difficult to obtain cell-free extracts of methane-utilizing bacteria which will oxidize methane reproducibly [l] . The extracts, however, showed methane-stimulated NADH oxidation [7] and CO-stimulated NADH oxidation [8] activities. The stoichiometry of these oxidations confirmed the involvement of a monooxygenase (hydroxylase) [2,9] : CH, + O2 + NADH + I-l++ CHsOH t NAD+ + Hz0 or CO + 02 + NADH + I-l+ COz + NAD+ + HzO. This paper reports the competitive inhibition of ammonia oxidation by methane, carbon monoxide or methanol and the presence of an ammonia-dependent NADH oxidation activity in Nitrosomonas extracts. Requirement for NADH or hydroxylamine as electron donor in ammonia oxidation is also demonstrated. The mechanism of ammonia oxidation is compared to that of methane oxidation.