Gentisate 12dioxygenase

Rhizobium leguminosarum enzyme is a dimer, molecular weight 120000 and optimum pH 9.5 [H127].

Gentisate 0 6-carboxy-4-hydroxy-cis, cis-

muconic semialdehyde (maleylpyruvate)

Pseudomonas acidovorans and P. testosteroni enzymes differ in molecular weight (164000 and 158 000, respectively) and amino acid composition. They are similar in requiring Fe2 +, and show a broad specificity toward substituted gentisates; 1,4-dihydroxy-2-naphthoate, an analogue of gentisate with a fused ring system, is also a substrate for the P. acidovorans enzyme [F649]. P. alcaligenes enzyme is a tetramer, molecular weight 154000, optimum pH 8 and pi 4.8-5.0. P. putida enzyme is a dimer, molecular weight 82000, optimum pH 8 and pi 4.6-4.8. Enzymes from both species are activated by Fe2+ [K4].

Klebsiella pneumoniae enzyme is a tetramer, molecular weight 159 000, optimum pH 8-9 and pi 4.7 [J246]. Bacillus stearothermophilis enzyme appears to be a hexamer, monomeric molecular weight 40 000 that requires Fe2+ [H893]. Rhodococcus erythropolis enzyme, a homooctamer, molecular weight 328 000, is activated by Fe2 +. Other substrates are gentisates substituted with methyl or halogen [H441].

2,3-Dihydroxy-p -cumate 3,4-dioxygenase

Bacillus enzyme has an optimum pH of 8.2. The reaction product is 3-carboxy-2-hydroxy-7-methyl-6-oxoocta-2,4-dienoate. Other substrates include pyrocatechuate, 3-methylcatechol, 3-iso-propylcatechol and 2,3-dihydroxy-^-toluate, but not catechol or 4-substituted catechols. This distinguishes the enzyme from catechol 2,3-dioxygenase [G766, G768].

Homogentisicase (homogentisate 1,2-dioxygenase; E.C. 1.13.11.5)

Homogentisate + O2 0 maleylacetoacetate

Rat liver enzyme shows a diurnal rhythm, with a sharp decrease in activity at 1800-2100, immediately after light is withdrawn. This coincides with maximal activity in the diurnal rhythm for tyrosine transaminase (E.C. 2.6.1.5) [A1060].

Mouse liver enzyme appears to be a homo-trimer, molecular weight 149000, optimum pH 6.1 and pi about 8. It has an absolute requirement for Fe2 + ; ascorbate is required, probably to keep Fe in the reduced form [H436].

Rabbit liver enzyme is a heterodimer monomeric molecular weight 230 000 and 200 000, and an optimum at about pH 5. It is also found in human embryo [H768].

A homogentisicase has been found in Drosophyllum lusitanicum [A1149].

Aspergillus enzyme requires Fe2+ ; other cations such as Fe3 + , Cu2 + , Co2+ and Mn2 + cannot substitute for Fe2+ . This enzyme is very labile in the presence of oxygen [B848]. Another study found that A. nidulans enzyme is 'rather stable' and highly specific [H900].

3,4-Dihydroxyphenylacetate 2,3-dioxygenase

3,4-Dihydroxyphenylacetate 0 S-carboxymethyl-a-hydroxy-cis, cis-muconic semialdehyde

Bacillus brevis enzyme is a tetramer, molecular weight 140000, with monomeric molecular weight 36 000. It is not activated by Fe2+ or inhibited by CN~ (atypical for this type of enzyme, which is usually activated by Fe2 + ), peroxide or diethyldithiocarbamate. it contains two mol of Mn/mol, probably as Mn2 +; it is claimed to be the first Mn-containing oxygen-activating enzyme described [B947]. it may utilize superoxide as co-substrate [B299].

Bacillus stearothermophilus enzyme is a globular protein, molecular weight 106 000,

3-Carboxyethylcatechol 2,3-dioxygenase composed of monomers, molecular weight 33 000-35 000, and is stable up to 55°. It acts on 3,4-dihydroxyphenylacetate, 3,4-dihydroxymandelate and dihydrocaffeate with a similar Vmax; protocatechuate is a poorer substrate. Catechol, 4-methylcatechol, L-dopa and dopamine are not substrates, indicating a narrower specificity than for enzyme from Pseudomonas ovalis. It shows a broad optimum about pH 8.4-8.7. Its amino acid composition has been determined [A2827].

Pseudomonas ovalis enzyme (colourless), is apparently a homopolymer, molecular weight 140 000 and monomeric molecular weight 35 000. It contains 4-5 mol of non-haem iron (Fe2 + ). Its amino acid composition has been determined, and the carbonyl terminal amino acid is leucine. Many catechols are substrates, but often with a very low oxidation rate. It is inactivated by oxygen or by other oxidizing agents; reactivation is brought about by Fe2+ or reducing agents, suggesting that inactivation involves oxidation to Fe3+ [A1090, A1230].

Klebsiella pneumoniae enzyme, a homotetra-mer, molecular weight 102000, requires four mol of Mg2+ mol [H232].

Arthrobacter synephrinum enzyme, molecular weight 282 000, additionally acts on 3,4-dihydroxymandelate and dihydrocaffeate [A3279].

3-Carboxyethylcatechol 2,3-dioxygenase

Achromobacter enzyme requires Fe2+ [K819].

Caffeate 3,4-dioxygenase (E.C. 1.13.11.22)

This reaction in Hydrogenophaga palleronii is catalyzed by protocatechuate 3,4-dioxygenase (see above) [J218].

L-Dopa 4,5-dioxygenase

Amanita muscaria enzyme is a heteropolymer, monomeric molecular weight 22000. The muco-

nic semialdehyde formed is an intermediate in the formation of betalamic acid. Other catechols are also substrates [G119].

Questin monooxygenase (E.C. 1.14.13.43)

Aspergillus terreus enzyme is composed of two proteins, optimum pH 7.5, requires oxygen and NADPH and is very unstable. The reaction involves opening the quinone ring to form a carboxylic acid [K701].

3,4-Dihydroxyphenylalanine: oxygen 2,3-oxidoreductase (recyclizing) (stizolobinate synthase, E.C. 1.3.11.30)

Stizolobium hassjoo seedling enzyme, optimum pH 7.6 is highly specific. It requires Zn2 + , is unstable especially in air and is inhibited by thiol-binding compounds [K706, K708].

3.4-Dihydroxyphenylalanine: oxygen

4.5-oxidoreductase (recyclizing) (stizolobate synthase, E.C. 1.3.11.29)

Stizolobium hassjoo seedling enzyme, optimum pH 7.4 is highly specific. It requires Zn2 + , is unstable especially in air and is inhibited by thiol-binding compounds [K706, K708].

1,2-Dihydroxynaphthalene oxygenase

Pseudomonas putida enzyme, molecular weight in excess of 275 000, and subunit molecular weight 19 000, yields 2-hydroxychromene-2-carboxylate, presumably a secondary product from cis-4-(o -hydroxyphenyl)-2-oxobut-3-enoate, the fission product. It requires Fe2 +; iron-binding compounds are inhibitory, and this is reversed by Fe2+. 3-Methylcatechol is also a substrate, but most other catechols are not [B527].

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