(Model) studies on vanadate-dependent bromo/iodoperoxidase from Ascophyllum nodosum VO 2+ 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. VO 2+ is only weakly associated to the surface of A,n.I. There is no transport channel for VO 2+. The EPR spectrum of the reduced holoenzyme is unisotropic (axial) already at room temperature, with EPR parameters similar to those of VO 2+ 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 H 2VO − 4 in water has also been investigated (by 51V NMR); the formation constant at pH 7.2 amounts to 266(28) M −1.