The inorganic biochemistry of molybdoenzymes

Bray, Robert C.

doi:10.1017/s0033583500004479

Cited by 184 publications

(172 citation statements)

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“…As already noted, our data relating to the glycol form of this signal differ importantly from those reported by Finnegan et al (1993) for R. sphaeroides Me,SO reductase treated with glycerol, though the signals themselves appear identical. Our findings of low conversion to the signal-giving species, retention of enzymic activity and loss of the signal on oxidation, all weaken the conclusion of these workers of a structural analogy to the very stable Desulpho-Inhibited species (Bray, 1988) for desulpho xanthine oxidase.…”

Section: Relations Of the Different Signal-giving Species To Meso Recontrasting

confidence: 60%

“…Spectra were transferred to a mainframe computer for g-scale alignment, background subtraction, integration and manual or iterative simulation. The software used (G. N. George, unpublished work) was as outlined by Bray and George (1985) and, where employed, difference techniques were as summarized by Bray (1988). g-Value estimates are believed to be accurate to ?0.0003 or better.…”

Section: 75mentioning

confidence: 99%

“…The changes in parameters are comparable (Table 2), when the Slow signal from desulpho xanthine oxidase is compared with the Rapid signal from this enzyme in the functional state. The corresponding structural change is presumed (Bray, 1988) to involve replacement of an -OH by an -SH ligand. Also comparable, are the parameters changes when the High-pH and Low-pH species from sulphite oxidase are considered, though here, in contrast, there is no information available other than the EPR parameters, supporting such a change of ligand (see George et al, 1989).…”

Section: General Structural Inferences From the Epr Parametersmentioning

confidence: 99%

“…The special contribution of EPR to molybdenum enzymes has depended on the narrow spectral linewidth shown by molybdenum in the molybdenum(V) oxidation state. Careful examination of the EPR spectra, malung use where appropriate of spectral deconvolution and simulation techniques Bray, 1988), has made it clear that the molybdenum centre of each enzyme studied in detail can exist in several different and clearly defined states, each producing its own charcteristic molybdenum(V) EPR signal. Much effort has been expended (e.g.…”

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Multiple States of the Molybdenum Centre of Dimethylsulphoxide Reductase from Rhodobacter Capsulatus Revealed by EPR Spectroscopy

Bennett

Benson

McEwan

et al. 1994

European Journal of Biochemistry

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137

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The dimethylsulphoxide reductase of Rhodobacter capsulatus contains a pterin molybdenum cofactor molecule as its only prosthetic group. Kinetic studies were consistent with re-oxidation of the enzyme being rate limiting in the turnover of dimethylsulphoxide in the presence of the benzyl viologen radical. EPR spectra of molybdenum(V) were generated by reducing the highly purified enzyme under a variety of conditions, and with careful control it was possible to generate at least five clearly distinct EPR signals. These could be simulated, indicating that each corresponds to a single chemical species. Structures of the signal-giving species are discussed in light of the EPR parameters and of information from the literature. Three of the signals show coupling of molybdenum to an exchangeable proton and, in the corresponding species, the metal is presumed to bear a hydroxyl ligand. One signal with g,, 1.96 shows a very strong similarity to a signal for the desulpho form of xanthine oxidase, while two others with g,, values of 1.98 show a distinct similarity to signals from nitrate reductase of Escherichia coli. These data indicate an unusual flexibility in the active site of dimethylsulphoxide reductase, as well as emphasising structural similarities between molybdenum enzymes bearing different forms of the pterin cofactor. Interchange among the different species must involve either a change of coordination geometry, a ligand exchange, or both. The latter may involve replacement of an amino acid residue co-ordinating molybdenum via 0 or N, for a cysteine co-ordinating via S. Since the two signals with g,, 1.96 were obtained only under specific conditions of reduction of the enzyme by dithionite, it is postulated that their generation may be triggered by reduction of the pteridine of the molybdenum cofactor from a dihydro state to the tetrahydro state.Enzymes that depend on the pterin molybdenum cofactor (Rajagopalan, 1991) are widely distributed, have a variety of important roles in different organisms and have been extensively studied in many laboratories (for recent reviews, see Spiro, 1985;Bray, 1988;Solomonson and Barber, 1990;Wootton et al., 1991 ;Enemark and Young, 1993). Detailed structural information from X-ray crystallography is not yet available on any of these enzymes (however, see Romao et al., 1993a,b). All but one of the enzymes contain, in addition to molybdenum, redox centres such as flavin, haem or ironsulphur. These complicate spectroscopic investigations and, in particular, their strong absorption in the ultraviolethisible region effectively masks the rather weak absorption of the molybdenum chromophore. Nevertheless, other spectroscopic methods have provided important insights into the local structure around the molybdenum atom. EPR spectroscopy has been very important in this context and has been supplemented particularly by extended X-ray absorption fine structure (EXAFS) and to a lesser extent by magnetic circular Abbreviations. MCD, magnetic circular dichroism ; EXAFS, extended X-ray absorpt...

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Section: Relations Of the Different Signal-giving Species To Meso Recontrasting

confidence: 60%

Section: 75mentioning

confidence: 99%

Section: General Structural Inferences From the Epr Parametersmentioning

confidence: 99%

mentioning

confidence: 99%

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Multiple States of the Molybdenum Centre of Dimethylsulphoxide Reductase from Rhodobacter Capsulatus Revealed by EPR Spectroscopy

Bennett

Benson

McEwan

et al. 1994

European Journal of Biochemistry

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137

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“…Each subunit contains one molybdenum, one FAD, and two nonidentical ironsulfur redox centers (1,2). Although it has broad specificities for both reducing and oxidizing substrates, its conventionally accepted role is in purine catabolism, where it catalyzes the oxidation of hypoxanthine to xanthine and xanthine to uric acid.…”

Section: Xanthine Oxidoreductase (Xor)mentioning

confidence: 99%

Reduction of Nitrite to Nitric Oxide Catalyzed by Xanthine Oxidoreductase

Godber¹,

Doel²,

Sapkota³

et al. 2000

Journal of Biological Chemistry

376

288

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Xanthine oxidase (XO) was shown to catalyze the reduction of nitrite to nitric oxide (NO), under anaerobic conditions, in the presence of either NADH or xanthine as reducing substrate. NO production was directly demonstrated by ozone chemiluminescence and showed stoichiometry of approximately 2:1 versus NADH depletion. With xanthine as reducing substrate, the kinetics of NO production were complicated by enzyme inactivation, resulting from NO-induced conversion of XO to its relatively inactive desulfo-form. Steady-state kinetic parameters were determined spectrophotometrically for urate production and NADH oxidation catalyzed by XO and xanthine dehydrogenase in the presence of nitrite under anaerobic conditions. pH optima for anaerobic NO production catalyzed by XO in the presence of nitrite were 7.0 for NADH and <6.0 for xanthine. Involvement of the molybdenum site of XO in nitrite reduction was shown by the fact that alloxanthine inhibits xanthine oxidation competitively with nitrite. Strong preference for Mo‫؍‬S over Mo‫؍‬O was shown by the relatively very low NADH-nitrite reductase activity shown by desulfo-enzyme. The FAD site of XO was shown not to influence nitrite reduction in the presence of xanthine, although it was clearly involved when NADH was the reducing substrate. Apparent production of NO decreased with increasing oxygen tensions, consistent with reaction of NO with XO-generated superoxide. It is proposed that XO-derived NO fulfills a bactericidal role in the digestive tract.

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