Kinetics of reduction by substrate or dithionite and heme-heme electron transfer in the multiheme hydroxylamine oxidoreductase

Hooper, Alan B.; Tran, Mai Van; Balny, Claude

doi:10.1111/j.1432-1033.1984.tb08230.x

Cited by 28 publications

(27 citation statements)

References 22 publications

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“…The remaining 0.2 heme equivalent of c-553 were reduced more slowly in phase 2. This biphasic phenomenon had been observed previously at atmospheric pressure although the values of rate costants are slightly different from those published by us some years ago [7]. As in the case of the kinetics of formation of the carboxylated enzyme, this may be due to the different buffer used.…”

Section: Kinetics Of Formation Of the Co-complex With Ferrous P460contrasting

confidence: 63%

“…The kinetics of reduction of c hemes of the enzyme with NHzOH consisted of two phases. Rate constants (designated k, and k,) and changes in absorbance during the phases (designated dAl and dA2) were calculated as described previously [7]. The apparent activation volumes ( A V * ) were calculated from the pressure-dependence of k l ,co,…”

Section: Determination Of Kinetic Constants and Activation Volumementioning

confidence: 99%

“…One explanation for the two phases of reduction of c hemes could invoke two sites of reaction of substrate with the enzyme; a highly specific substrate site containing P460 and one (or more) less specific second sites [7]. According to this model, k l or k z could represent kinetic constants associated with the reaction of NHzOH at each of these sites.…”

Section: Ejject Of Pressure On the Binding Of Co To Ferrous P460 Of Hmentioning

confidence: 99%

“…According to this model, k l or k z could represent kinetic constants associated with the reaction of NHzOH at each of these sites. This model is unlikely to apply since NHzOH does not react at the second site(s) [7]. An alternative model suggests that the enzyme can exist in at least two states, differing in the rate of heme-heme electron transfer.…”

Section: Ejject Of Pressure On the Binding Of Co To Ferrous P460 Of Hmentioning

confidence: 99%

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Effect of solvent, pressure and temperature on reaction rates of the multiheme hydroxylamine oxidoreductase

Balny

Hooper

1988

European Journal of Biochemistry

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Hydroxylamine oxidoreductase (HAO) of the ammonia-oxidizing bacterium Nitrosomonas catalyzes the oxidation: N H 2 0 H + H 2 0 + HNOz + 2e-+ 2 H'. The heme-like chromophore P460 is part of a site which binds substrate, extracts electrons and then passes them to the many c hemes of the enzyme. Reduction of the c hemes by hydroxylamine is biphasic with apparent first-order rate constants kl and k z . CO binds to ferrous P460 with apparent first-order rate constants, kl,co. In this work we have measured the binding of CO to ferrous P460 of hydroxylamine oxidoreductase and the reduction by substrate of some of the 24 c hemes of the ferric enzyme. These reactions have been studied in water and 40% ethylene glycol, at temperatures ranging from -15°C to 2 0 . 7 T and at hydrostatic pressures ranging over 0.1 -80 MPa. From the measurements, thermodynamic parameters A V* (activation volume), AG*, AH', and AS* have been calculated.CO binding. Binding of CO to ferrous P460 was similar to the binding of CO to ferrous horseradish peroxidase. The change of solvent had only a limited effect on A V* (-30 ml . mol-I), AG", AH* or AS* and did not cause an inflection in the Arrhenius plot or downward displacement of the linear relationship between In kl,co and P at a critical temperature. Binding was exothermic at high temperatures. The response of the binding of CO to solvent, temperature and pressure suggested that the CO binding site had little access to solvent and was not susceptible to change in protein conformation.Fast phase of reduelion of c hemes. Changing the solvent from water to 40% ethylene glycol resulted in a decrease from 90% to 50% in the relative number of c hemes reduced during the fast phase, an increase in activation volume from -3.6 ml . mol-' to 57 ml . mol-' and changes in other thermodynamic parameters. The activation volume increased with decreasing temperature. The Arrhenius plot had a downward inflection at about 0°C and, in water or ethylene glycol, the linear dependence of In kl on P was displaced downwards as the temperature changed from 3.5"C to -15°C.Slow phase of reduction of c hemes. Changing the solvent from water to 40% ethylene glycol resulted in an increase in the relative number of c hemes reduced during the slow phase from 10% to 50%. The activation volume, which was not measurable in water because of the low absorbance change, was -30 ml . mo1-l in ethylene glycol. The activation volume increased with increasing temperature. The Arrhenius plot had a downward inflection at about 0 "C yet the linear dependence of In k2 on P had no downward displacement in this temperature range. At high pressure and low temperatures the rate of heme reduction increased with decreasing temperature. In contrast to the reaction of CO with the substrate site, the results suggested that changes in enzyme conformation imposed by changes in solvent, temperature or pressure affected the rates of intramolecular electron transfer from the substrate site to c hemes.Hydroxylamine oxidoreductase from the ammonia-oxidizin...

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Section: Kinetics Of Formation Of the Co-complex With Ferrous P460contrasting

confidence: 63%

Section: Determination Of Kinetic Constants and Activation Volumementioning

confidence: 99%

Section: Ejject Of Pressure On the Binding Of Co To Ferrous P460 Of Hmentioning

confidence: 99%

Section: Ejject Of Pressure On the Binding Of Co To Ferrous P460 Of Hmentioning

confidence: 99%

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Effect of solvent, pressure and temperature on reaction rates of the multiheme hydroxylamine oxidoreductase

Balny

Hooper

1988

European Journal of Biochemistry

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“…Also chemolithotrophic, nitrifying bacteria possess complex arrangements of internal membranes (54). Spheroplasts of Nitrosomonas do not contain internal vesicles (55). This suggests that internal membranes of those organisms are invaginations.…”

Section: Magnetosome-specific Gtpasementioning

confidence: 94%

A Magnetosome-specific GTPase from the Magnetic BacteriumMagnetospirillum magneticum AMB-1

Okamura

Takeyama

Matsunaga

2001

Journal of Biological Chemistry

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Magnetic bacteria produce intracellular vesicles that envelope single domain magnetite crystals. Although many proteins are present in this intracellular vesicle membrane, five are specific to this membrane. A 16-kDa protein, designated Mms16, is the most abundant of the magnetosome-specific proteins, and to establish its function we cloned and sequenced its gene from Magnetospirillum magneticum AMB-1. This was achieved by determination of the N-terminal amino acid sequence of the protein following two dimensional polyacrylamide gel electrophoresis, and sequencing of the gene was performed by gene walking using anchored polymerase chain reaction. Mms16 contains a putative ATP/GTP binding motif (P-loop). Recombinant Mms16 with a hemagglutinin tag, was expressed in Escherichia coli and purified. Recombinant Mms16 protein could bind GTP and showed GTPase activity. GTP was the preferred substrate for Mms16-catalyzed nucleotide triphosphate hydrolysis. These results suggest that a novel protein specifically localized on the magnetic particle membrane, Mms16, is a GTPase. Mms16 protein showed similar characteristics to small GTPases involved in the formation of intracellular vesicles. Furthermore, addition of the GTPase inhibitor AlF 4 ؊ also inhibited magnetic particle synthesis, suggesting that GTPase is required for magnetic particles synthesis.Magnetic bacteria synthesize intracellular magnetite particles that are aligned in chains of around 10 particles per cell. They are covered with a thin lipid membrane and have an average diameter of 50 -100 nm. The morphology of these bacterial magnetic particles (BMPs) 1 is species-dependent, and it is therefore reasonable to hypothesize that species-specific biological factors located in the BMP membrane mediate magnetite crystallization (1). However, the mechanism of BMP synthesis, including vesicle formation, still remains unclear. A complete understanding of biomineralization and of membrane vesicle formation at the molecular level will also have important implications for studying biomineralization in general and vesicle formation in prokaryotes in particular.Several processes are involved in BMP synthesis, and one of the most important is vesicle formation. Numerous studies have been devoted to the investigation of eukaryotic intracellular vesicle formation, and hence the molecular machinery is well understood (for reviews, see Refs. 2 and 3). In contrast, there are few molecular studies of vesicle formation or of the events leading to invagination of the cytoplasmic membrane in prokaryotes. We have hypothesized that the BMP membrane is derived from the cytoplasmic membrane and formed through the invagination of the cytoplasmic membrane by a process similar that which occurs in eukaryotes (4).A second process in BMP synthesis is magnetite crystallization, and this has been studied in more detail. It appears that ferric iron is reduced on the cell surface, taken into the cytoplasm, transferred into vesicles (magnetosomes), and finally oxidized to produce magnetite (5...

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Hydroxylamine Oxidoreductase

Igarashi¹,

Tanaka²

2004

Handbook of Metalloproteins

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as hydroxylamine oxidase (HAO).Hydroxylamine oxidoreductase (HAO) catalyzes the fourelectron oxidation of hydroxylamine to nitrite. The enzyme shows a high biologically specificity. The most efficient oxidizing substrate is hydroxylamine, and no other nitrogen compound except for hydrazine reacts with 3D Structure Schematic representation of the trimer structure of HAO from N. europaea. Each subunit is a single color (yellow, blue, pink). The hemes are shown in red ball-and-stick representation. Prepared with programs molscript 58 and raster3d. 59 The PDB code is 1FGJ.

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Kinetics of reduction by substrate or dithionite and heme-heme electron transfer in the multiheme hydroxylamine oxidoreductase

Cited by 28 publications

References 22 publications

Effect of solvent, pressure and temperature on reaction rates of the multiheme hydroxylamine oxidoreductase

Effect of solvent, pressure and temperature on reaction rates of the multiheme hydroxylamine oxidoreductase

A Magnetosome-specific GTPase from the Magnetic BacteriumMagnetospirillum magneticum AMB-1

Hydroxylamine Oxidoreductase

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