The function of the iron centers of the bacterial catechol dioxygenase enzymes in dioxygen activation was studied. The enzymes were found to convert dihydroxybenzenes into nonaromatic, acyclic compounds, which were then utilized as carbon sources for cell growth. Although these enzymes shared similar substrates, the intradiol- and extradiol-cleving enzymes exhibited near exclusivity in their oxidative cleavage products. The intradiol-cleaving catechol dioxygenases were also found to use an [Fe iii-(His) 2] active site, while extradiol-cleaving catechol dioxygenases contained a [M ii(His) 2(Asp/Glu)] active site.