Judith M. Arber

A structural model for vanadyl–histidine interactions: structure determination of [VO(1-vinylimidazole)4Cl]Cl by a combination of X-ray crystallography and X-ray absorption spectroscopy

[VO(1-vinylimidazole)4Cl]Cl is prepared and spectroscopically characterized and structural information obtained from vanadium K-edge EXAFS used to solve a disorder problem encountered in the refinement of the crystal structure; oxovanadium(IV) bound to imidazole groups has relevance to the possible biochemical functions of vanadium.

Characterization of molybdenum and vanadium centres in enzymes by X-ray absorption spectroscopy

Metal K-edge EXAFS studies have provided the only structural evidence so far available for the molybdenum and vanadium centres in enzymes. This paper describes the results of vanadium and iron K-edge EXAFS on the iron-molybdenum and iron-vanadium cofactors of the nitrogenase enzymes for Klebsiella pneumoniae and Azotobacter chroococcum, respectively, and the vanadium K-edge EXAFS of the bromoperoxidase from Ascophyllum nodosum. These and other results suggest that molybdenum and vanadium sites in enzymes may be classified in a similar manner: (a) as part of an Fe3MS4 (M = Mo, V) cubane-like cluster which forms a sub-unit of the cofactor of the nitrogenases; (b) bound to one (or more) oxo groups plus sulphur (in the case of molybdenum) or oxygen/nitrogen (in the case of vanadium) ligands to form a catalytic centre for oxygen atom transfer.

EXAFS studies of metallothionein

Extended x-ray absorption fine structure (EXAFS) has been used to investigate the metal environment in a number of metallothioneins (MT). In all cases, the primary coordination sphere consists of sulphur atoms. In some cases, evidence for cluster formation is obtained.

X-Ray Absorption Spectroscopic Studies of Vanado-Enzymes: Nitrogenase and Bromoperoxidase

Vanadium is well recognised as an essential trace element, is widely distributed throughout the lithosphere and biosphere, and is present in all mammalian tissues at concentrations of ≤ 10μM (Chasteen, 1983). However, only in a few instances can a precise biological role be assigned to this element. It is a potent inhibitor of phosphatases, Na,K-ATPases, and a variety of other important enzymes, doubtless because of the similarity of AO4 3- (for A=V or P) and their derivatives. Amavadin, an oxovanadium(IV) complex with two molecules of N-(1-carboxyethyl)-N-hydroxyalanine, has been isolated from the mushroom Amanita muscaria (Kneifel and Bayer, 1986) and may function as an electron-transfer catalyst (Nawi and Riechel, 1987). Two enzyme systems were shown to be dependent upon vanadium: nitrogenases from Azotobacter (Robson et al., 1986) and bromoperoxidases from marine algae (de Boer et al., 1986; de Boer et al., 1986). Herein we describe the results of vanadium K-edge X-ray absorption spectroscopic studies for a member of each of these two types of vanadium-dependent enzymes.