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Wever
Brominating Activity of the Seaweed Ascophyllum nodosum: Impact on the BiosphereRon Wever, Michiel G. M. Tromp, Bea E. Krenn, Abdoeljallal Marjani, and Mauritz Van Tol Environ. Sci. Technol. 1991, 25, 446-449
"Macroalgae are an important source of volatile halogenated organic compounds, such as bromoform and dibromomethane. The mechanism by which these compounds are formed is still elusive. We report that the brown seaweeds Laminaria saccharina, Laminaria digitata, Fucus uesiculosis, Pelvetia canaliculata, and Ascophyllum nodosum and the red seaweeds Chondrus crispus and Plocamium hamatum contain bromoperoxidases. The intact plants are able to brominate exogeneous organic compounds when HzO, and Br- are added to seawater. Further, we show that the brominating activity of the brown macroalga A. nodosum, which contains a vanadium bromoperoxidase located on the thallus surface, occurs when the plant is exposed to light and not in the dark. The rate of bromination of exogenous organic compounds in seawater by this plant is 68 nmol (g of wet alga1-l h-l. HOBr is a strong biocidal agent and we propose that the formation of HOBr by this seaweed is part of a host defense system."
Structure and function of vanadium-containing bromoperoxidases.Wever R, Krenn BE, De Boer E, Offenberg H, Plat H. Prog Clin Biol Res. 1988;274:477-93. [abstract only]
"The properties of the vanadium-containing bromoperoxidases from the seaweeds Ascophyllum nodosum, Laminaria saccharina and the lichen Xanthoria parietina were studied. Upon reduction with sodium dithionite, these bromoperoxidases show EPR spectra which are typical of a vanadyl cation (VO2+). From the spectral parameters and a comparison with inorganic vanadyl complexes, we conclude that the ligand environment largely consists of oxygen donors. The data also show that the structure of the active sites in these enzymes is very similar. Since EPR spectra of vanadium(IV) bromoperoxidase are only obtained after reduction, the metal ion is present in the native enzymes in the 5+ oxidation state. All these enzymes loose their enzymic activity upon dialysis against citrate-phosphate (PO4(3-)) buffer at pH 3.8, containing EDTA. The brominating activity could be reconstituted by the addition of vanadate (VO4(3-)). The experiments suggest that vanadate is incorporated into these enzymes. In line with the EPR data, we propose a structure of the active site in which at least 4 oxygen atoms are present as donors for the central vanadium(V) ion. Since several inorganic peroxovanadium(V) complexes have been described, we suggest that the vanadium ion in bromoperoxidases serves as a binding site for H2O2. Upon subsequent binding of bromide this ion is oxidized by the peroxo-intermediate to form hypobromite. This model does not require valence state changes of the metal ion itself and indeed no changes in the EPR spectrum of reduced bromoperoxidase are observed upon addition of H2O2 or Br-. Further, bromoperoxidase reduced with a small excess of sodium dithionite is not active in the bromination reaction. The bromoperoxidases from the various sources show similarity in the amino-acid composition with a predominance of acidic amino acids. Distinct pH optima are observed in the bromination reaction catalysed by the bromoperoxidases. Despite the presence of the same prosthetic group in these enzymes with comparable vanadium ligand-field environment, the enzymic properties are very different. The specific activity as well as the Km for bromide differ greatly. Unlike the enzymes from the seaweeds A. nodosum and L. saccharina the bromoperoxidase from the lichen X. parietina is inhibited by low concentrations (1-5 mM) of nitrate. These bromoperoxidases have a remarkable resistance towards organic solvents such as methanol, ethanol and propanol."
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