| Abstract
| - Density functional theory has been used to investigate structural, electronic and reactivityproperties of complexes related to the peroxo forms of vanadium haloperoxidases (VHPO). In particular,the reactivity of the cofactor as a function of protonation state and environment, which are two factorsthought to be crucial in modulating the activity of the enzyme, has been examined. In full agreement withexperimental data, results highlight the role of protonation in the activation of the peroxo-vanadium complexesand show that the oxo-transfer step involves the unprotonated axial peroxo oxygen atom, which is easilyaccessible to substrates in the peroxo form of the enzyme. The role of Lys353, which in the X-ray structureof the peroxide-bound form of vanadium chloroperoxidase is hydrogen bonded to the equatorial oxygenatom of the peroxo group, has been also explored. It is concluded that Lys353 can play a role similar to aH+ in the activation of the peroxo form of the cofactor.
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