Summary: Chloroperoxidase (CPO) is a 42 kDa Da extracellular heme glycoenzyme containing ferriprotoporphyrin IX as the prosthetic group. CPO is secreted from fungus and exhibits a broad spectrum of chemical reactivities. It is a peroxide-dependent chlorinating enzyme. It also catalyzes peroxidase-, catalase-and cytochrome P450-type reactions of dehydrogenation, H2O2 decomposition and oxygen insertion, respectively. The enzyme has magnetic and spectroscopic properties similar to that of cyctochrome P-450. CPO from the fungus Caldariomyces fumago has the capacity to chlorinate aromatic hydrocarbons, including polycyclic aromatic hydrocarbons (PAHs).