Abstract
Vanadate(V)-dependent haloperoxidases VHPOs in marine macroalgae catalyze the 2e- oxidation, by H2O2, of bromide and iodide (X-) to X+ species such as HOX, X2 and X3-. Several other substrates, including sulfides, are also oxidized. In the active center, H2VO4- is covalently attached to the Ne of a histidine residue, an arrangement that has successfully been modeled with synthetic analogs of the active center. Vanadium acts as a Lewis acid, forming an intermediate peroxido/hydroperoxido complex. The X+ species generated by the VHPOs halogenates organics present in seawater, from which halomethanes CH4-nXn (n is chiefly 2 or 1) evolve. Additionally, the hypohalous acids can protect the algae against biofilm formation. Prospective applications point towards this biocidal (anti-bacterial) potential of the peroxidases. The seaweeds further exploit the haloperoxidase activity in the synthesis of a multitude of brominated bio-functional molecules. Algal bromoperoxidase activity may account for up to 25% of the atmospheric bromine load. Bromomethanes and iodine released from the aqua- into the atmosphere substantially contribute to ozone depletion, and thus indirectly also to the oxidative conversion of (atmospheric) dimethyl sulfide and nitric oxide.
Published Version
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