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

Abstract
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 unisotropic (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 H2VO 4 in water has also been investigated (by 51V NMR); the formation constant at pH 7.2 amounts to 266(28) M−1.

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