Aromatic Hydrocarbon Dioxygenases

Abstract

Since the initial discovery of toluene dioxygenase (TDO) by David Gibson and coworkers (Yeh et al. 1977; Subramanian et al. 1979), aromatic hydrocarbon dioxygenases have been reported to catalyze the initial reaction in the bacterial biodegradation of a diverse array of aromatic and polyaromatic hydrocarbons, aromatic acids, chlorinated aromatic, and heterocyclic aromatic compounds. To date, more than 100 aromatic compound dioxygenases have been described in the literature based on biological activity or nucleotide sequence identity. These enzymes are cofactor-requiring multicomponent heteromultimeric proteins (EC 1.14.12) that catalyze the initial activation through reductive dihydroxylation of their substrates, and are distinct from aromatic ring-cleavage (or ring-fission) dioxygenases (EC 1.13.11), which act on the catechol intermediates in many of the same catabolic pathways. This chapter will focus primarily on the aromatic ringhydroxylating dioxygenases (Rieske non-heme iron dioxygenases; EC 1.14.12), which initiate an attack on aromatic hydrocarbons, heterocycles and related compounds carrying various substituents (Cl, NO2). The aspects described will relate to dioxygenase discovery, classification, enzymology, structure, electron transport, mechanism and applications.