Abstract
Polycyclic aromatic hydrocarbons (PAHs), such as naphthalene, are potential health risks due to their carcinogenic and mutagenic effects. Bacteria from the genus Rhodococcus are able to metabolise a wide variety of pollutants such as alkanes, aromatic compounds and halogenated hydrocarbons. A naphthalene dioxygenase from Rhodococcus sp. strain NCIMB12038 has been characterised for the first time, using electron paramagnetic resonance (EPR) spectroscopy and UV-Vis spectrophotometry. In the native state, the EPR spectrum of naphthalene 1,2-dioxygenase (NDO) is formed of the mononuclear high spin Fe(III) state contribution and the oxidised Rieske cluster is not visible as EPR-silent. In the presence of the reducing agent dithionite a signal derived from the reduction of the [2Fe-2S] unit is visible. The oxidation of the reduced NDO in the presence of O2-saturated naphthalene increased the intensity of the mononuclear contribution. A study of the “peroxide shunt”, an alternative mechanism for the oxidation of substrate in the presence of H2O2, showed catalysis via the oxidation of mononuclear centre while the Rieske-type cluster is not involved in the process. Therefore, the ability of these enzymes to degrade recalcitrant aromatic compounds makes them suitable for bioremediative applications and synthetic purposes.
Highlights
Polycyclic aromatic hydrocarbons (PAHs) arise from diverse sources, including petrochemical products and the combustion of fossil fuels [1]
“peroxide shunt”, an alternative mechanism for the oxidation of substrate in the presence of H2 O2, showed catalysis via the oxidation of mononuclear centre while the Rieske-type cluster is not involved in the process
The PAH naphthalene is released into the environment as coal tar and coal tar products such as creosote [2], and bacteria which degrade naphthalene are widely distributed in nature [3]
Summary
Polycyclic aromatic hydrocarbons (PAHs) arise from diverse sources, including petrochemical products and the combustion of fossil fuels [1]. Mononuclear iron of separate subunits within ∼12Å, which is a reasonable distance for electron This allows room for a “bridge” between the Rieske cluster of one unit and the iron active site. Rieske cluster is connected to the neighbouring subunit mononuclear iron—believed to be the oxygen site. The crystal structure of free and substrate-bound forms of naphthalene dioxygenase gating electron transport [10]. The crystal the substrate indole binds near the mononuclear iron suggesting that this is the site for the oxygen structure showed that the substrate indole binds near the mononuclear iron suggesting that this is bonding [14]. The general accepted catalytic cycle for electrons and an oxygen molecule to hydroxylate the naphthalene substrate. [16,17]
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