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Biomedical subjects

A V Xavier

Publications and source records attributed to A V Xavier.

At least 127 records · Page 7Linked to original sources
PubMed1978

Oxidation-reduction studies of the Mo-(2Fe-2S) protein from Desulfovibrio gigas.

Potentiometric titration followed by e.p.r. measurements were used to determine the midpoint reduction potentials of the redox centres of a molybdenum-containing iron-sulphur protein previously isolated from Desulfovibrio gigas, a sulphate-reducing bacterium (Moura, Xavier, Bruschi, Le Gall, Hall & Cammack (1976) Biochem. Biophys. Res. Commun. 728 782-789; Moura, Xavier, Bruschi, Le Gall & Cabral (1977) J. Less Common Metals 54, 555-562). The iron-sulphur centres could readily be distinguished into three types by means of g values, temperature effect, oxidation-reduction potential values and reduction rates. The type-I Fe-S centres are observed at 77 K. They show mid-point potential values of -260mV (Fe-S type IA) and -440 mV (Fe-S type IB). Centres of types IA and IB appear to have similar spectra at 77 K and 24 K. The Fe-S type-II centres are only observed below 65 K and have a midpoint potential of -28mV. Long equilibration times (30 min) with dye mediators under reducing conditions were necessary to observe the very slow equilibrating molybdenum signals. The potential values associated with this signal were estimated to be approx. -415 mV for Mo(VI)/Mo(V) and-530mV for Mo(V)/Mo(IV).

Desulfovibrio↗
PubMed1978

A comparative spectroscopic study of two non-haem iron proteins lacking labile sulphide from Desulphovibrio gigas.

The ultraviolet visible, and near infrared spectrum of a two-iron protein from Desulphovibrio gigas, a new type of non-haem iron protein lacking labile sulphide, is compared with that of D. gigas rubredoxin. The charge transfer band maxima of rubredoxin at 495 and 565 nm are less separated in the new protein implying a higher symmetry of the two iron centres. The existence of a spin-spin interaction between the two iron centres in the new protein is suggested by the magnetic susceptibility measurements of the oxidized and reduced states of both proteins, which gives a smaller value per iron centre for the new protein. The oxidized form of the two iron-protein has a complex EPR spectrum with signals at g values of 8.97, 7.72, 5.73, 4.94, and 1.84. An EPR titration gives a value of --35 +/- 15 mV for the two signals at g values of 7.72 and 5.73. Rubredoxin has the characteristic spectrum of rubredoxins with two signals at g values of 9.4 and 4.27.

Bacterial Proteins↗
PubMed1978

EPR determination of the oxidation-reduction potentials of the hemes in cytochrome c3 from Desulfovibrio vulgaris.

EPR spectroscopy in conjunction with oxidation-reduction potentiometry has been used to determine the half-reduction potentials of the four hemes of cytochrome c3. As predicted, the four hemes of cytochrome c3 have different mid-point potentials. The Em values are: Heme I,--284 mV; Heme II,--310 mV; Heme III,--324 mV and Heme IV,--319 mV. The n-values in each case was near one.

Cytochrome c Group↗
PubMed1978

NMR studies of electron carrier proteins from sulphate reducing bacteria.

The sulphate-reducing bacteria have a complex electron transfer system which leads to the reduction of sulphate by oxidation of either organic substrates or molecular hydrogen. These bacteria can either produce or consume molecular hydrogen. The central part of this electron pathway for Desulovibrio gigas is constituted by hydrogenase (3 X (4Fe-4S)). cytochrome c3 (4 haems with different redox potentials) and a one (4Fe-4S) cluster ferredoxin. This ferredoxin is isolated in different oligomeric forms, which stabilize different oxidation states and have different physiological roles; the trimer FdI being involved in the production of H2 and the tetramer FdII being more efficient for the consumption of H2. The presence of intrinsic probes (the iron ions) in these proteins is particularly helpful for structural studies using NMR spectroscopy. These studies allowed a characterization of the oxidation states used by the different oligomers of the ferredoxin and obtaintion of structural information on multi-haem cytochromes (c3 and c7). NMR is also suitable to study protein-protein interaction. The study of the complex formed between FdII and cytochrome c3 has shown that there is an alteration of the kinetics of electron transfer upon complexation.

Carrier Proteins↗
PubMed1977

Spectroscopic studies of the oxidation-reduction properties of three forms of ferredoxin from Desulphovibrio gigas.

Electron paramagnetic resonance spectra were recorded of three forms of Desulphovibrio gigas ferredoxin, FdI, FdI' and FdII. The g = 1.94 signal seen in dithionite-reduced samples is strong in FdI, weaker in FdI' and very small in FdII. The g = 2.02 signal in the oxidized proteins is weak in FdI and strongest in FdII. It is concluded that most of the 4Fe-4S centres in FdI change between states C- and C2-; FdI' contain both types of centre. There is no evidence that any particular centre can change reversibly between all three oxidation states. Circular dichroism spectra show differences between FdI and FdII even in the diamagnetic C2- state. The redox potentials of the iron-sulphur centres of the three oligomers (forms) are different. After formation of the apo-protein of FdII and reconstitution with iron and sulphide, the protein behaves more like FdI, showing a strong g = 1.94 signal in the reduced states.

Binding Sites↗
PubMed1977

NMR characterization of three forms of ferredoxin from Desulphovibrio gigas, a sulphate reducer.

A NMR and magnetic susceptibility study of the oxidized and reduced states of three different oligomers (forms) of a [4Fe-4S] ferrodoxin protein from Desulphovibrio gigas, FdI, FdI', and FdII was carried out. FdI and FdI' are different trimers and FdII a tetramer of the same basic subunit. A probable assignment of the contact shifted resonances is indicated. Since the temperature dependences of the contact shifted responances associated with each [4Fe-4S] are not all similar a delocalized model for the spin densities on the 4Fe does not apply. The exchange rate between oxidized and reduced states is slow on the NMR time scale. The three oligomers are not magnetically equivalent. Using the "three state hypothesis" terminology it is shown that FdIox is predominantly in the C2- state and changes upon reduction into the C3- state, while FdIIox is in the C- state and changes into the C2- state. FdI' does not easily fit into this classification. This study shows a similarity of magnetic behaviour between FdI and bacterial ferredoxins (e.g. Bacillus polymyxa) and between FdII and HiPIP from Chromatium sp. The influence of the quaternary structure on the stabilization of the different oxidation states of ferredoxins as well as on their redox potentials is discussed.

Desulfovibrio↗
PubMed1976

Purification, characterization and biological activity of three forms of ferredoxin from the sulfate-reducing bacterium Desulfovibrio gigas.

Three forms of ferredoxin FdI, FdI', and FdII have been isolated from Desulfovibrio gigas, a sulfate reducer. They are separated by a combination of DEAE-cellulose and gel filtration chromatographic procedures. FdI and FdI' present a slight difference in isoelectric point which enables the separation of the two forms over DEAE-cellulose, while FdII is easily separated from the two other forms by gel filtration. The three forms have the same amino acid composition and are isolated in different aggregation states. Molecular weight determinations by gel filtration gave values of 18 000 for FdI and FdI' and 24 000 for FdII, whereas a value of 6000 is determined when dissociation is accomplished with sodium dodecyl sulfate. The electronic spectra are different and their ultraviolet-visible absorbance rations are 0.77, 0.87 and 0.68 respectively for FdI, FdI' and FdII. Despite these differences, the physiological activities of the three forms are similar as far as the reduction of sulfite by molecular hydrogen is concerned.

Amino Acids↗