Hydroxylamine oxidoreductase from Nitrosomonas: absorption spectra and content of heme and metal

Hooper, Alan B.; Maxwell, Peter; Terry, Kathleen R.

doi:10.1021/bi00608a007

Cited by 95 publications

(76 citation statements)

References 20 publications

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“…Spectra shown in Fig. 1 closely resemble dithionite-reduced minus dithionite-reduced-plus-CO spectra of resting enzyme [3] or P460 polypeptide [6]. A difference spectrum of identical shape was obtained instantaneously after flash photolysis of reduced CO-liganded enzyme.…”

Section: Reaction Of Heme P460 Of H a 0 With Comentioning

confidence: 88%

“…Ferrous P460 of H A 0 will reduce 0, [12]; thus c hemes of the enzyme may serve as a steady-state 'pool' of reductant for 0, activation by heme P460. HAO-P460 reduces H,O, at rates high enough to account for the rate of oxygen activation for nitrite synthesis during turnover of H A 0 (and H A 0 activity can account for the rate of nitrite production by intact cells [3]). The turnover of HAO, 120mol NH,OH s-' mol P-460-', would require the one-electron activation of dioxygen at a rate of 120 rnol s -' rnol P460-I (NH,OH+Fe"'+'/, 0, 4 HNO, …”

Section: Discussionmentioning

confidence: 99%

“…Pure hydroxylamine oxidoreductase (HAO) was prepared from Nitrosomonas europaea as described previously ; the concentration of H A 0 in the oxidized form was determined using the absorption coefficient, E~~~, of 2000 mM cm-' [3]. For destruction of P460, resting H A 0 (1.5 pM) in phosphate buffer was treated with 100pM H,02 for 30min at room temperature [5].…”

Section: Enzymementioning

confidence: 99%

“…The reaction sequence probably includes removal of hydrogen from hydroxylamine for production of a proton gradient and subsequent production of ATP. During oxidation of ammonia to nitrite by Nitrosomonus at least one oxygen atom comes from dioxygen [I, 21. Hydroxylamine oxidoreductase (HAO) catalyzes oxidation of hydroxylamine (NH,OH) to nitrite in the presence of dioxygen and an appropriate electron acceptor [3]. In solution the enzyme consists of three 1 1 000-M, mono-heme c cytochrome and three polypeptides, M , 74000, each containing six c hemes and one heme P460 [4].…”

mentioning

confidence: 99%

“…P460, a CO-binding pigment which is unique to the ammonia-oxidizing bacteria, copurifies with hydroxylamine oxidoreductase and has absorption maxima at 463 nm and 447 nm, respectively, in the dithionite-reduced or dithionitereduced-plus-CO forms [3,61. The P460 iron center is EPRsilent in oxidized H A 0 [7] but is identified with a g = 6 center following reduction of approximately 80 % of the c hemes with dithionite [S].…”

mentioning

confidence: 99%

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Heme P460 of Hydroxylamine Oxidoreductase of Nitrosomonas

Hooper

Debey

Andersson

et al. 1983

European Journal of Biochemistry

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Hydroxylamine oxidoreductase (HAO) of Nitrosomonas catalyzes the dehydrogenation of NH2OH and subsequent addition of oxygen to form nitrite. HAO contains c hemes and the CO‐binding heme P460 in a 7:1 ratio; dehydrogenation of NH2OH involves passage of electrons to P460 and then c hemes. We now report that electrons rapidly pass from c hemes of HAO to the P460 center and then to H2O2. This conclusion is supported by (a) inhibition of c heme oxidation with CO and (b) loss of H2O2‐oxidizability of ferrous c hemes following specific destruction of heme P460. Reaction of ferrous P460 with H2O2 is rate‐limiting. Activation of dioxygen for N‐oxidation by ferrous HAO may involve the two‐electron reduction of O2 by P460. The reaction of ferrous HAO with H2O2 was studied as it may reveal aspects of the mechanism of activation of dioxygen. Reaction of ferrous heme P460 with CO is slow and with low affinity as compared with other hemoproteins. Values for reaction of CO with enzyme were: k1, 1.1 × 10−3 M−1 s−1 and Kd, 12μM.

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Section: Reaction Of Heme P460 Of H a 0 With Comentioning

confidence: 88%

Section: Discussionmentioning

confidence: 99%

Section: Enzymementioning

confidence: 99%

mentioning

confidence: 99%

mentioning

confidence: 99%

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Heme P460 of Hydroxylamine Oxidoreductase of Nitrosomonas

Hooper

Debey

Andersson

et al. 1983

European Journal of Biochemistry

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Cytochromec₅₅₄

Iverson¹,

Hendrich²,

Arciero³

et al. 2004

Handbook of Metalloproteins

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Cytochrome c 554 (cyt c 554 ) is a tetra‐heme c ‐type cytochrome that participates in the nitrification pathway of Nitrosomonas europaea . In this process, cyt c 554 functions as the electron acceptor from the enzyme hydroxylamine oxidoreductase that catalyzes the oxidation of hydroxylamine to nitrite. Cyt c 554 is a predominantly α‐helical protein with four covalently attached hemes. The four hemes are arranged in two pairs, such that the planes of the porphyrin rings are nearly parallel and overlapping at the edges. This type of heme‐stacking has been observed in two other nitrogen cycle proteins: hydroxylamine oxidoreductase and cytochrome c nitrite reductase, an enzyme that catalyzes the reduction of nitrite to ammonia. The relatively unusual spectral properties of cyt c 554 may reflect interactions between these pairs of stacked hemes.

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