Nocardioides enzyme, monomeric molecular weight 45 000 and native molecular weight 270 000, contains one mol Fe2 + /mol, which is essential for activity. The product is 4-(o -carboxyphenyl)-2-oxobutyrate [J598].
Coccus enzyme requires oxygen and is activated by Fe2+ [E730].
Diphenyl ether fission
Rat liver converts thyroxine into diiodotyrosine; the reaction requires oxygen [C809]. It is also catalyzed by human thyroid peroxidase [D553].
Pseudomonas cruciviae degrades diphenyl ether to phenol, probably with 2-phenoxymuco-nate as an intermediate [E41].
o -Aminophenol 1,6-dioxygenase
Pseudomonas arvilla pyrocatechase oxidizes the substrate to 2-aminomuconic semialdehyde [A3636]. P. pseudoalcaligenes enzyme, molecular weight 140 000 and monomeric molecular weights 35 000 and 39 000, requires oxygen , with an apparent requirement for Fe2+. It also acts on catechol, 6-amino-3-methylphenol, 2-amino-3-methylphenol and 2-amino-4-chlorophenol, but other catechols and quinols are not substrates [J255, J329].
A bacterial enzyme, molecular weight 140000 and optimum pH 7.5 is stable between pH 7.5 and 9 [H915].
The rat brain and liver enzymes, molecular weight 37 000-38 000, appear to be identical. It has a broad optimum at about pH 6 /5 [E472]. Baboon liver enzyme has a similar molecular weight, optimum pH 7.4-7.6. It requires Fe2 + for activity [A2280] as do the vervet monkey and rat liver enzymes [A912, E114]. The latter enzyme exists as several isozymes. Beef kidney enzyme has a molecular weight of 34 000, and readily polymerizes to an inactive form [A2430].
Hydrogenophaga palleronii protocatechuate 3,4-dioxygenase acts on 4-sulphocatechol as well as on protocatechuate, dopac, caffeate and some neutral catechols. Its molecular weight is 97 000 and is composed of monomers, molecular weights 23 000 and 28 500. The product is 3-sulphomuconate [J218].
Chlorocatechol 2,3-dioxygenase (catechol 1,6-dioxygenase)
Pseudomonas putida enzyme is a tetramer, monomeric molecular weight 33 400 and pI 7.1. Other substrates include catechol, and catechols substituted with methyl or halogen. Although the product formed from 3-chlorocatechol is 2-hydroxymuconic acid indicating the formation of the acid chloride by proximal fission, the product formed from 3,5-dichlorocatechol indicates distal (1,6) fission. This enzyme is atypical for extradiol dioxygenases in that it is rapidly inactivated above 40° [J515].
Chlordiazon catechol dioxygenase
Phenylobacterium immobilis enzyme, pI 4.5, contains one Fe/subunit, and has been crystallized. The product is a hydroxymuconic semialdehyde [C332].
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