Flavoprotein dioxygenases

The external flavoprotein dioxygenases function by catalyzing the transfer of electrons from reduced nicotinamides to the aromatic nuclei of the substrate. The resulting radical anions would be sufficiently soft to react with molecular oxygen without requiring any particular assistance from the enzymes. 

An iron sulfur-flavoprotein that transfers electrons directly to the dioxygenase, as in phthalate dioxygenase (class I)... 

A flavoprotein that transfers electrons to the ferredoxin, as in benzene dioxygenase (class II)... 

Dioxygenases that form ds-diols are composed of two or three components, forming ds-dihydrodiols or ds-diol carboxylic acids, respectively. The three-component dioxygenases are composed of a flavoprotein, a ferredoxin, and a terminal oxygenase. 

I, 2-diol and NAD. This multiprotein complex contains an iron-sulfur flavoprotein, an iron-sulfur oxygenase, and ferredoxin. See also Phthalate Dioxygenase... 

Benzoate 1,2-dioxygenase [EC 1.14.12.10], also called benzoate hydroxylase, catalyzes the reaction of benzoate with dioxygen and NADH to generate catechol, carbon dioxide, and NAD+. This is a multiprotein system which contains a reductase which is an iron-sulfur flavoprotein (FAD) and an iron-sulfur oxygenase. 

It should be noted that non-heme oxygenases can also degrade aromatics such as biphenyls and naphthalene (Scheme 7.23). A naphthalene dioxygenase consists of a catalytic oxygenase component with a mononuclear iron site, an iron-sulfur flavoprotein reductase and an iron-sulfur ferredoxin transferring electrons from... 

The other classes of flavoproteins in table 10.2 interact with molecular oxygen either as the electron-acceptor substrates in redox reactions catalyzed by oxidases or as the substrate sources of oxygen atoms for oxygenases. Molecular oxygen also serves as an electron acceptor and source of oxygen for metalloflavoproteins and dioxygenases, which are not listed in the table. These enzymes catalyze more complex reactions, involving catalytic redox components, such as metal ions and metal-sulfur clusters in addition to flavin coenzymes. 

Gassner, G. T., Ludwig, M. L., Gatti, D. L., Correll, C. C., and Ballou, D. P., 1995, Stracture and mechanism of the iron-sulfur flavoprotein phthalate dioxygenase reductase. FASEB J. 9 1411nl418. 

Naphthalene dioxygenase consists of three components, which form an electron transfer chain an NADH-dependent flavoprotein reductase, a ferredoxin containing two [2Fe2S] Rieske iron-sulfur clusters, and a Rieske oxygenase containing both a [2Fe2S] Rieske iron-sulfiir cluster and a mononuclear iron(II) center in the enzyme active site. ° ... 

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