Haloperoxidasen aus Braunalgen

(Model) studies on vanadate-dependent bromo/iodoperoxidase from Ascophyllum nodosum. VO2+ is not incorporated into the active site

Vanadate-dependent peroxidase A.n.I, the main isoenzyme (M(r) = 100 kDa) from the seaweed, Ascophyllum nodosum, contains 2 V per enzyme molecule (as shown by ICP-MS metal analysis) after complete reconstitution with vanadate (V), possibly distributed in a 1:1 ratio between the surface and active site. VO2+ is only weakly associated to the surface of A.n.I. There is no transport channel for VO2+. The EPR spectrum of the reduced holoenzyme is anisotropic (axial) already at room temperature, with EPR parameters similar to those of VO2+ complexes of small model peptides such as Ala-His, Gly-Tyr, Gly-Ser, Gly-Glu, Ser-Gly and Phe-Glu. The complex formation between Ala-His and H2VO4- in water has also been investigated (by 51V NMR); the formation constant at pH 7.2 amounts to 266(28) M-1.

Structure and function of vanadium compounds in living organisms

Vanadium has been recognized as a metal of biological importance only recently. In this mini-review, its main functions uncovered during the past few years are addressed. These encompass (i) the regulation of phosphate metabolizing enzymes (which is exemplified for the inhibition of ribonucleases by vanadate), (ii) the halogenation of organic compounds by vanadate-dependent non-heme peroxidases from seaweeds, (iii) the reductive protonation of nitrogen (nitrogen fixation) by alternative, i.e. vanadium-containing, nitrogenases from N2-fixing bacteria, (iv) vanadium sequestering by sea squirts (ascidians), and (v) amavadine, a low molecular weight complex of V(IV) accumulated in the fly agaric and related toadstools. The function of vanadium, while still illusive in ascidians and toadstools, begins to be understood in vanadium-enzyme interaction. Investigations into the structure and function of model compounds play an increasingly important role in elucidating the biological significance of vanadium.