Electron paramagnetic resonance and potentiometric studies of arsenite interaction with the molbydenum centers of xanthine oxidase, xanthine dehydrogenase, and aldehyde oxidase: a specific stabilization of the molybdenum(V) oxidation state

Biochemistry ◽  
1983 ◽  
Vol 22 (3) ◽  
pp. 618-624 ◽  
Author(s):  
Michael J. Barber ◽  
Lewis M. Siegel
Keyword(s):  
Electron Paramagnetic Resonance ◽  
Xanthine Oxidase ◽  
Oxidation State ◽  
Aldehyde Oxidase ◽  
Xanthine Dehydrogenase ◽  
Potentiometric Studies ◽  
Paramagnetic Resonance ◽  
Electron Paramagnetic

scholarly journals Studies by electron-paramagnetic-resonance spectroscopy on the mechanism of action of xanthine dehydrogenase from Veillonella alcalescens

1976 ◽  
Vol 153 (2) ◽  
pp. 287-295 ◽  
Author(s):  
H Dalton ◽  
D J Lowe ◽  
R T Pawlik ◽  
R C Bray
Keyword(s):  
Electron Paramagnetic Resonance ◽  
Electron Paramagnetic Resonance Spectroscopy ◽  
Aldehyde Oxidase ◽  
Detailed Comparison ◽  
Xanthine Dehydrogenase ◽  
Resonance Spectroscopy ◽  
Enzyme Complex ◽  
Partial Reduction ◽  
Paramagnetic Resonance ◽  
Electron Paramagnetic

E.p.r- (electron-paramagnetic-resonance) spectroscopy was used to compare chemical environment and reactivity of molybdenum, flavin and iron-sulphur centres in the enzyme xanthine dehydrogenase from Veillonella alcalescens (Micrococcus lactilyticus) with those of the corresponding centres in milk xanthine oxidase. The dehydrogenase is frequently contaminated with small but variable amounts of a species resistant to oxidation and giving a new molybdenum (V) e.p.r. signal, “Resting I”. There is also a “desulpho” form of the enzyme giving a Slow Mo(V) signal, indistinguishable from that of the milk enzyme. Molybdenum of the active enzyme behaves in a manner analogous to that of the milk enzyme, giving a Rapid Mo(V) signal on partial reduction with substrates or dithionite. Detailed comparison shows that molybdenum in each enzyme must have the same ligand atoms arranged in the same manner. As with the milk enzyme, complex-formation between reduced dehydrogenase and purine substrate molecules, presumably interacting at the normal substrate-binding site, modifies the Rapid signal, confirming that such substrates interact near molybdenum. The dehydrogenase-flavin semiquinone signal is identical with that of the oxidase but, in contrast, there is only one iron-sulphur signal. The latter gives an e.p.r. spectrum similar to that of aldehyde oxidase.

scholarly journals A new non-functional form of milk xanthine oxidase containing stable quinquivalent molybdenum

1976 ◽  
Vol 155 (1) ◽  
pp. 81-85 ◽  
Author(s):  
D J Lowe ◽  
M J Barber ◽  
R T Pawlik ◽  
R C Bray
Keyword(s):  
Ethylene Glycol ◽  
Xanthine Oxidase ◽  
Functional Form ◽  
Aldehyde Oxidase ◽  
Xanthine Dehydrogenase ◽  
Resonance Signal ◽  
Paramagnetic Resonance ◽  
Step Process ◽  
Nitrogen Ligand ◽  
Electron Paramagnetic

A new non-functional modified form of milk xanthine oxidase is described. This contains molybdenum in a quinquivalent state, which is resistant to both oxidation and reduction. The new species is derived from the native enzyme in a two-step process. The first step is the conversion into the desulpho form, via loss of the ‘persulphide’ sulphur, and the second involves reaction with ethylene glycol or other reagents. The species gives a characteristic Mo(V) electron-paramagnetic-resonance signal, without proton splittings, designated Resting II. This is virtually identical with signals reported previously from resting turkey liver xanthine dehydrogenase and rabbit liver aldehyde oxidase. The possibility is discussed that species Resting II, prepared with ethylene glycol, contains a -COCH2OH residue bound to a nitrogen ligand of molybdenum.

scholarly journals Studies by electron-paramagnetic-resonance spectroscopy and stopped-flow spectrophotometry on the mechanism of action of turkey liver xanthine dehydrogenase

1976 ◽  
Vol 153 (2) ◽  
pp. 297-307 ◽  
Author(s):  
M J Barber ◽  
R C Bray ◽  
D J Lowe ◽  
M P Coughlan
Keyword(s):  
Electron Paramagnetic Resonance ◽  
Redox Potential ◽  
Active Sites ◽  
Electron Paramagnetic Resonance Spectroscopy ◽  
Xanthine Dehydrogenase ◽  
Resonance Spectroscopy ◽  
Stopped Flow ◽  
Paramagnetic Resonance ◽  
Flow Measurements ◽  
Electron Paramagnetic

Studies by e.p.r. (electron-paramagnetic-resonance) spectroscopy and by stopped-flow spectrophotometry on turkey liver xanthine dehydrogenase revealed strong similarities to as well as important differences from the Veillonella alcalescens xanthine dehydrogenase and milk xanthine oxidase. The turkey enzyme is contaminated by up to three non-functional forms, giving molybdenum e.p.r. signals designated Resting I, Resting II and Slow. Slow and to a lesser extent Resting I signals are like those from the Veillonella enzyme, whereas Resting II is very like a resting signal described by K. V. Rajagopolan, P. Handler, G. Palmer & H. Beinert (1968) (J. Biol. Chem. 243, 3784-3796) for aldehyde oxidase. Another non-functional form that gives the Inhibited signal is produced on treatment of the enzyme with formaldehyde. Stopped-flow measurements at 450 nm show that, as for the milk enzyme, reduction by xanthine is rate-limiting in enzyme turnover. The active enzyme gives rise to Very Rapid and Rapid molybdenum(V) e.p.r. signals, as well as to an FADH signal. That these signals are almost indistinguishable from those of the milk enzyme, confirms the similarities between the active sites. There are two types of iron-sulphur centres that give signals like those in the milk enzyme, though with slightly different parameters. Quantitative reduction titration of the functional enzyme with xanthine revealed two important differences between the turkey and the milk enzymes. First, the turkey enzyme FADH/FADH2 system has a redox potential sufficiently low that xanthine is incapable of reducing the flavin completely. This finding presumably explains the very low oxidase activity. Secondly, whereas the Fe/S II chromophore in the milk enzyme has a relatively high redox potential, for the turkey enzyme the value of this potential is lower and similar to that of its Fe/S I chromophore.

scholarly journals Magnetic coupling of the molybdenum and iron-sulphur centres in xanthine oxidase and xanthine dehydrogenases

1978 ◽  
Vol 169 (3) ◽  
pp. 471-479 ◽  
Author(s):  
D J Lowe ◽  
R C Bray
Keyword(s):  
Xanthine Oxidase ◽  
Magnetic Coupling ◽  
Magnetic Interaction ◽  
Xanthine Dehydrogenase ◽  
Resonance Signal ◽  
Guanidinium Chloride ◽  
Paramagnetic Resonance ◽  
Interacting Species ◽  
Small Change ◽  
Electron Paramagnetic

Magnetic interaction between molybdenum and one of the iron-sulphur centres in milk xanthine oxidase [Lowe, Lynden-Bell & Bray (1972) Biochem. J. 130, 239-249] was studied further, with particular reference to the newly discovered Mo(V) e.p.r.(electron-paramagnetic-resonance) signal, Resting II [Lowe, Barber, Pawlik & Bray (1976) Biochem. J. 155, 81-85]. E.p.r. measurements at 35GHz near to 4.2K showed that the interaction has the same sign at all molybdenum orientations and is ferromagnetic. The predicted splitting of the e.p.r. signal from the reduced iron-sulphur centre, Fe/S I, was observed, Providing positive identification of this as the other interacting species. Chemical modification of the molybdenum environment in xanthine oxidase can change the size of the interaction severalfold, but interaction always remains approximately isotropic. The interaction in turkey liver xanthine dehydrogenase is indistinguishable from that in the oxidase. However, a bacterial xanthine dehydrogenase with different iron-sulphur centres shows rather larger interaction. Guanidinium chloride disturbs the iron-sulphur centres of the oxidase, and when this occurs there is a parallel and relatively small change in the interaction. Removal of flavin from the molecule, or raising the pH to 12.0, changes the interaction slightly without affecting the chromophores themselves. It is concluded that the Fe/S I centre and the Mo are at least 1.0nm and probably nearer 2.5nm apart, and that the conformation of the protein between them is relatively stable up to pH 12.

Electron paramagnetic resonance and potentiometric studies of the interactions of Cr(VI) and Cr(V) with d-ribose 5-phosphate and nucleotides

Polyhedron ◽  
2000 ◽  
Vol 19 (4) ◽  
pp. 417-423 ◽  
Author(s):  
Marcela Rizzotto ◽  
Virtudes Moreno ◽  
Sandra Signorella ◽  
Verónica Daier ◽  
Luis F Sala
Keyword(s):  
Electron Paramagnetic Resonance ◽  
Potentiometric Studies ◽  
Paramagnetic Resonance ◽  
Electron Paramagnetic
Sign in / Sign up

Export Citation Format

Share Document