Catechol 23dioxygenase

A. calcoaceticus enzyme, molecular weight 81 000-85 000 (using different measuring techniques), is composed of two monomers and contains two mol Fe/mol. Additional substrates (poor) are 3- and 4-methylcatechol and 3-iso-propylcatechol, but a number of other catechols are not substrates. It has a broad optimum at pH 7-9, which coincides with its stability range. Its amino acid composition has been determined; methionine is the amino terminal residue [A2640].

Rhizobium leguminosarum enzyme is a homodimer, molecular weight 70 000 and optimum pH 9-9.5, which contains one mol Fe/mol [F647]. R. trifolii enzyme is also a dimer, molecular weight 107000, containing 1 mol Fe3 + /mol monomer [D672].

Candida tropicalis enzyme, optimum pH 7.6-8.0, acts on catechol, 4-methylcatechol, 3-and 4-chlorocatechol but not on other catechols [E204].

Trichosporon cutaneum enzyme has molecular weight 105 000 and 35 000 for holoenzyme and monomer respectively. Its specificity is broad, acting on catechol, 4-methylcatechol, pyrogallol and hydroxyquinol [C84].

Pseudomonas pyrocatechase II acts on catechols substituted at positions 3 and 4 with methyl, chloro or fluoro groups [B754]. P. arvilla enzyme converts pyrogallol into both a-hydroxymuconic acid and 2-pyrone-6-carboxylic acid; the latter is formed by ring closure of the ring fission product, possibly without prior release from the enzyme [B547].

Brevibacterium enzyme contains Fe3 +, apparently sulphur-bound [A1231].

Enzyme from an unspecified bacterium has an optimum between pH 7 and 10 [B525].

Catechol 2,3-dioxygenase (metapyrocatechase; E.C.

Catechol 0 2-hydroxymuconic semialdehyde

A study carried out on extradiol dioxygenases from a series of 7 Pseudomonas strains demonstrated that each enzyme has its own quantitative specificity towards catechol, 3-

and 4-methylcatechol, 4-chlorocatechol and 2,3-dihydroxybiphenyl, ranging from good activity for most of these substrates to good activity for only 2,3-dihydroxybiphenyl [H272]. One Pseudomonas enzyme is a homotetramer, with apparent molecular weight for monomer and tetramer of 33 000 and 110000, respectively. Its optimum pH is 8-8.5 and is stable up to 70°. It acts on catechol, 3- and 4-methylcatechol; 3-fluorocatechol, and 4-chlorocatechol are poor substrates [J649]. Another study by the same research team confirmed many of these results, but gave a tetrameric molecular weight of 120 000 [G355]. P. putida enzyme is probably a homo-tetramer with subunit molecular weight 34 000 [K204].

P. arvilla enzyme oxidizes pyrogallol to a-hydroxymuconic acid [B547] and is inhibited competitively by o -nitrophenol or m -phenanthroline relative to catechol, but non-competitively relative to oxygen [A1031]. It is not inhibited by superoxide dismutase (E.C., hence, superoxide is not the oxidizing species, nor by compounds capable of trapping singlet oxygen [A1047]. P. aeruginosa enzyme is inhibited by ATP and Mg2+ [A2832].

Bacillus thermoleovorans enzyme is a homo-tetramer, subunit molecular weight 34 700, pI 4.8, optimum pH 7.2, and contains one Fe/monomer. It is inactivated rapidly at 70° [K228].

Enzyme from a thermophilic Bacillus is inactivated by high concentrations of oxygen [J834].

Hydroxyquinol 1,2-dioxygenase (E.C.

Burkholderia cepacia enzyme is a dimer, molecular weight 68 000. It is highly specific, forming maleylacetate [J251].

Azotobacter enzyme is a dimer, monomeric molecular weight 34 000, which is activated by Fe2+. An additional substrate is 6-chloro-1,2,4-trihydroxybenzene [H602].

Phanerochaete chrysosporium enzyme is a dimer, molecular weight 90 000. It incorporates molecular oxygen into the product. It is highly specific, but also oxidizes catechol [H284].

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