oxygen, Fe
2+ and reduced pyridine nucleotides. Ring hydroxylating dioxygenases
are soluble, multicomponent enzyme systems that are comprised of two or three
separate proteins. These dioxygenases consist of an electron transport chain where
electrons from NAD(P)H are channelled to the catalytic terminal oxygenase component for substrate transformation. The catalytic terminal oxygenase component
contains a cluster [Rieske (2Fe-2S)] and mononuclear iron called Rieske nonhaeme iron oxygenase (Gibson and Parales 2000).
Generally, the electron transport chain consists of either an iron–sulphur flavoprotein reductase or a flavoprotein reductase and an iron–sulphur ferredoxin; however, the structure of ring hydroxylating oxygenase is considerably different. These
enzymes have been classified as Class I, II, III based on the variation in number and
the size of constituent compounds and their nature of redox centre (Batie and Kamin
Fig. 14.2 Multiple pathways for dibenzofuran degradation: Dibenzofuran {product A} Mono
hydroxy dibenzofuran {product b, c, d and e}; 2,2
0 ,3-trihydroxybiphenyl {n}; 2-hydroxy-6-(2hydroxyphenyl)-6-oxo-2,4–5 hexadienoic acid (2
0 -OH-HOPDA) {product P}; 2
0 -Hydroxy aceto
phenone{product z}; 3-(Chroman-4-on-2-yl)pyruvic acid {product z1}; chromone {product z2};
Salicylic acid {product z3}; 2,4-hexadienoic acid {product z4}; Gentesic acid {product z5};
Catechol {product z6}; 1,2-dihydro-1,2-dihydroxydibenzofuran {product u}; 3,4-dihydro-1,2dihydroxy dibenzofuran {product l}; 2’hydroxy-4-(3
0 -oxo-3’H-benzofuran-2
0 -yliden)but-2-enoic
acid or (3
0 -HOBB) {product x}; 2
0 hydroxy-4-(2
0 -oxo-2’H-benzofuran-3
0 -yliden)but-2-enoic acid or
(2
0 -HOBB) {product w} and 2-(1-carbonyl methylidine)-2,3-dihydrobenzofuran lidene-glycolic
acid {product v}. 1-hydroxydibenzofuran {product b}; 2-hydroxydibenzofuran {product c}; 3hydroxydibenzofuran {product d}; 4-hydroxydibenzofuran {product e}; riboside conjugate of 2hydroxydibenzofuran {product h}; riboside conjugate of 3-hydroxydibenzofuran {product k};
2,8-dihydroxydibenzofuran {product o}; 2,7-dihydroxydibenzofuran, {product g}; 3,7dihydroxydibenzofuran {product I}; [2-(1-carboxymethylidene)-6-hydroxy-benzofuran-3ylidene]-hydroxyacetic acid {product S};benzo[b]furo[3,2-d]-2-pyrone-6-carboxylic acid
{product y}
14 Metabolism of Dioxins and Dioxins-Like Compound, Its Regulation and. . .
301
2+ and reduced pyridine nucleotides. Ring hydroxylating dioxygenases
are soluble, multicomponent enzyme systems that are comprised of two or three
separate proteins. These dioxygenases consist of an electron transport chain where
electrons from NAD(P)H are channelled to the catalytic terminal oxygenase component for substrate transformation. The catalytic terminal oxygenase component
contains a cluster [Rieske (2Fe-2S)] and mononuclear iron called Rieske nonhaeme iron oxygenase (Gibson and Parales 2000).
Generally, the electron transport chain consists of either an iron–sulphur flavoprotein reductase or a flavoprotein reductase and an iron–sulphur ferredoxin; however, the structure of ring hydroxylating oxygenase is considerably different. These
enzymes have been classified as Class I, II, III based on the variation in number and
the size of constituent compounds and their nature of redox centre (Batie and Kamin
Fig. 14.2 Multiple pathways for dibenzofuran degradation: Dibenzofuran {product A} Mono
hydroxy dibenzofuran {product b, c, d and e}; 2,2
0 ,3-trihydroxybiphenyl {n}; 2-hydroxy-6-(2hydroxyphenyl)-6-oxo-2,4–5 hexadienoic acid (2
0 -OH-HOPDA) {product P}; 2
0 -Hydroxy aceto
phenone{product z}; 3-(Chroman-4-on-2-yl)pyruvic acid {product z1}; chromone {product z2};
Salicylic acid {product z3}; 2,4-hexadienoic acid {product z4}; Gentesic acid {product z5};
Catechol {product z6}; 1,2-dihydro-1,2-dihydroxydibenzofuran {product u}; 3,4-dihydro-1,2dihydroxy dibenzofuran {product l}; 2’hydroxy-4-(3
0 -oxo-3’H-benzofuran-2
0 -yliden)but-2-enoic
acid or (3
0 -HOBB) {product x}; 2
0 hydroxy-4-(2
0 -oxo-2’H-benzofuran-3
0 -yliden)but-2-enoic acid or
(2
0 -HOBB) {product w} and 2-(1-carbonyl methylidine)-2,3-dihydrobenzofuran lidene-glycolic
acid {product v}. 1-hydroxydibenzofuran {product b}; 2-hydroxydibenzofuran {product c}; 3hydroxydibenzofuran {product d}; 4-hydroxydibenzofuran {product e}; riboside conjugate of 2hydroxydibenzofuran {product h}; riboside conjugate of 3-hydroxydibenzofuran {product k};
2,8-dihydroxydibenzofuran {product o}; 2,7-dihydroxydibenzofuran, {product g}; 3,7dihydroxydibenzofuran {product I}; [2-(1-carboxymethylidene)-6-hydroxy-benzofuran-3ylidene]-hydroxyacetic acid {product S};benzo[b]furo[3,2-d]-2-pyrone-6-carboxylic acid
{product y}
14 Metabolism of Dioxins and Dioxins-Like Compound, Its Regulation and. . .
301