ChemInform Abstract: LONG RANGE ELECTRON PARAMAGNETIC RESONANCE COUPLING INTERACTIONS IN SPIRO DERIVATIVES OF BICYCLO(2,2,1)HEPTY SEMIQUINONE

1975 ◽  
Vol 6 (46) ◽  
pp. no-no
Author(s):  
D. KOSMAN ◽  
L. M. STOCK
Keyword(s):  
Electron Paramagnetic Resonance ◽  
Long Range ◽  
Paramagnetic Resonance ◽  
Spiro Derivatives ◽  
Resonance Coupling ◽  
Electron Paramagnetic ◽  
Derivatives Of

scholarly journals Coupling of [33S]sulphur to molybdenum(V) in different reduced forms of xanthine oxidase

1981 ◽  
Vol 199 (3) ◽  
pp. 629-637 ◽  
Author(s):  
J P G Malthouse ◽  
G N George ◽  
D J Lowe ◽  
R C Bray
Keyword(s):  
Electron Paramagnetic Resonance ◽  
Xanthine Oxidase ◽  
The Other ◽  
Reduced Form ◽  
Sulphur Atom ◽  
Paramagnetic Resonance ◽  
Different Types ◽  
Resonance Coupling ◽  
Electron Paramagnetic ◽  
Reduced Forms

Different reduced forms of xanthine oxidase, labelled specifically in the cyanide-labile site with 33S, were prepared and examined by electron paramagnetic resonance. Coupling of this isotope to molybdenum(V) was quantified with the help of computer simulations and found to differ markedly from one reduced form to another. The xanthine Very Rapid signal shows strong, highly anisotropic, coupling with A(33S)av. 1.27 mT. For this signal, axes of the g- and A(33S)-tensors are rotated relative to one another. One axis of the A-tensor is in the plane of gxx ang gyy, but rotated by 40 degrees relative to the gxx axis, whereas the direction of weakest coupling to sulphur deviates by 10 degrees from the gzz axis. In contrast with this signal, only rather weaker coupling was observed in different types of Rapid signal [A(33S)av. 0.3--0.4 mT], and in the Inhibited signal coupling was weaker still [A(33S)av. 0.1--0.2 mT]. Clearly, there must be substantial differences in the structures of the molybdenum centre in the different signal-giving species, with the sulphur atom perhaps in an equatorial type of ligand position in the Very Rapid species but in a more axial one in the other species. Structures are discussed in relation to the mechanism of action of the enzyme and the nature of the proton-accepting group that participates in turnover.

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