Atypical kinetic behavior of chloroperoxidase-mediated oxidative halogenation of polycyclic aromatic hydrocarbons.

We have identified an atypical kinetic behavior for the oxidative halogenation of several polycyclic aromatic hydrocarbons (PAHs) by chloroperoxidase (CPO) from Caldariomyces fumago. This behavior resembles the capacity of some members of the P450 family to simultaneously recognize several substrate molecules at their active sites. Indeed, fluorometric studies showed that PAHs exist in solution as monomers and pi-pi dimers that interact to different extents with CPO. The dissociation constants of dimerization were evaluated for every single PAH by spectrofluorometry. Furthermore, docking studies also suggest that CPO might recognize either one or two substrate molecules in its active site. The atypical sigmoidal kinetic behavior of CPO in the oxidative halogenation of PAHs is explained in terms of different kinetic models for non-heteroatomic PAHs (naphthalene, anthracene and pyrene). The results suggest that the actual substrate for CPO in this study was the pi-pi dimer for all evaluated PAHs.