Pathways for BaP metabolism and detoxification.

BaP is metabolized into BaP-7,8-diol by cytochrome P450 (CYP450) and epoxide hydroxylase (EPHX) in a two-step reaction. BaP reactive metabolites, such as BaP-7,8-diol-9,10 epoxide (BaPDE) can form adducts with DNA, causing mutagenesis. The reactive metabolites generated can be inactivated via conjugation with glutathione (GSH) by glutathione S-transferase (GST). Reactions involved in glutathione synthesis for which up-regulated proteins were identified by BaP treatment are shown inside the grey box and include Serine hydroxymethyltransferase (SHMT) and O-acetylserine lyase (OASL). Alternatively, BaP-7,8-diol can be converted to catechol by a dihydrodiol dehydrogenase (DDH), which can be oxidized to BaP-7,8-dione. Produced reactive oxigen species (ROS) can be detoxified by the action of several enzymes, including ascorbate peroxidase (APX). Enzymes coding genes up-regulated in BaP-exposed diatoms are shown in a black box.