Peptide tryptophan 23dioxygenase

Peptide tryptophan 2,3-dioxygenase

Wheat germ (optimum pH about 8) and rat liver enzymes act on tryptophan residues in polypeptides such as pepsin and trypsin, converting them into kynurenine residues [K823].

Indole + O20 anthranilate

In rat, indole is converted into N-formylanthranilate, which is the expected initial product of indole ring fission, as well as anthranilate [D158].

Jasminum grandiflorum leaf enzyme, optimum pH 4.8, forms anthranilate from the substrate. Other substrates are 5-hydroxy- and 5-bromoindole. FAD is co-substrate and Cu2+ is also required; Cu2 +-chelating reagents are inhibitory [B70].

Tecoma stans leaf enzyme, optimum pH 5.2, utilizes two molecules of oxygen. Other substrates are 5-hydroxyindole, 5-bromoindole and 5-methylindole. It is not inhibited by thiols or by thiol-binding reagents, copper or non-haem iron chelators, nor by atebrin, which suggests that it is not a flavoprotein. It is inactivated by dialysis, but the cofactor has not been identified [C170].

Zea mays leaf enzyme, molecular weight 98 000, exhibits an optimum at pH 5.0. The initial product appears to be 2-formamidobenzaldehyde, although the products detected are anthranil and anthranilate; their formation requires four oxygen atoms. Copper-binding reagents are inhibitors, reversible by Cu2+ , which also activates dialyzed enzyme [D334].

Aspergillus niger forms both N-formylanthranilate and anthranilate, and enzymes for both reactions were found [F417].

A similar reaction occurs in wheat seedling, converting skatole into o -formamidoacetophe-none. The enzyme, which is composed of two isozymes, is different from tryptophan 2,3-dioxygenase [C559].

Indoleamine 2,3-dioxygenase (E.C. 1.13.11.42)

Mouse liver indoleamine 2,3-dioxygenase is totally different from rat liver tryptophan 2,3-dioxygenase, although tryptophan is the substrate. It is induced by lipopolysaccharide (which suppresses tryptophan 2,3-dioxygenase) and is found in almost all tissues examined, except trachea, bladder and spleen. In most tissues the activity is low, but good activity is found in lung, colon, liver, caecum, seminal vesicle and especially in epididymis [E30].

2,3-Dihydroxyindole 2,3-dioxygenase

A microorganism enzyme, optimum pH 8.0 and stable at pH 7 /9, requires oxygen. Analogues of the substrate are not oxidized [K821].

Quinaldate 4-oxidoreductase (E.C. 1.3.99.18)

Alcaligenes enzyme, molecular weight 155 000, requires oxygen and NADH, and is activated by Fe2+ . The reaction product is kynurenate [J32].

Pseudomonas enzyme, optimum pH 8.0, pi 4.6 and molecular weight 300 000, is composed of subunits, molecular weights 90 000, 34 000 and 20 000 (consistent with a a2p2g2 structure), contains molybdenum, iron, acid labile sulphur and FAD. It forms kynurenic acid from quinaldate. Heavy metals are inhibitory [K768].

Serratia marcescens enzyme (inducible), molecular weight 95000-100 000 is a heterodimer, monomeric molecular weights 75 000 /80 000 and 18 000-19 000; it contains Fe and Mo [K770].

7,8-Dihydroxykynurenate 8,8a-dioxygenase

This reaction forms 5-(3-carboxy-3-oxopropenyl)-4,6-dihydroxypyridine-2-carboxylate. The enzyme (source unstated) requires oxygen and NAD(P)H [K853].

Coumarin 3,4-oxide fission

Coumarin 3,4-oxide fission

This compound rapidly degrades to o -hydroxyphenylacetaldehyde in aqueous solution; it is postulated that this is an integral step in the route by which coumarin is degraded by mouse liver microsomes [H807].

Quercetin 2,3-dioxygenase (E.C. 1.13.11.24)

Aspergillus flavus enzyme contains copper but not iron. The products are 2-protocatechuoylphloroglucinolcarboxylic acid and carbon monoxide [K820].

Catechin oxygenase

Chaetomium cupreum enzyme, molecular weight 40000, optimum pH 7.0 and pI 9.1, is a glycoprotein and is specific for catechin. The reaction products are catechol, protocatechuate and phloroglucinolcarboxylate [G814].

2-Hydroxychromene-2-carboxylate isomerase

Pseudomonas enzyme, molecular weight 25 000-27 000 and optimum pH about 8, is stable at pH 3 /10. Glutathione appears to be both cofactor and stabiliser (at 50°). The reaction product is o-hydroxybenzylidenepyruvate, and lies on the degradation pathway of Tobias acid to salicylate [J711].

Maackiain fission

Stemphylium botryosum reductively opens the furan ring to form 2',7-dihydroxy-4',5'-methylenedioxyisoflavan [A2283].

Flavonol 2,4-dioxygenase

Aspergillus niger enzyme grown on rutin is a trimer, molecular weight 130 000-170000 (clearly a mixture), monomeric molecular weights about

65000, 55 000 and 33 000. It is a copper-containing glycoprotein composed of about 50 per cent N-linked oligomannose-type glycan chains. The products from quercetin are carbon monoxide and protocatechuoylphloroglucinol-carboxylate. It is potently inhibited by ethylxanthate, which specifically reduces Cu2+. It is inhibited by diethyldithiocarbamate without loss of copper [K214].

(+)-Pinoresinol/(+)-lariciresinol reductase

Forsythia intermedia enzyme is composed of two isozymes, molecular weight 35 000, separable by anion-exchange chromatography. The reaction involves the successive fission of both ether rings in pinoresinol to larisiresinol and (—)-secoisolarisiresinol [H883].

Usnic acid dehydrogenases ((S)-usnate reductase, E.C. 1.1.1.199)

Evernia prunastri enzyme, molecular weight 450 000, requires NADH for the reduction of l-usnic acid. d-Usnic acid dehydrogenase is composed of two isozymes. The reaction results in the opening of the ether ring [B774, E126].

Phosphoribosyl isomerisation

Phosphoribosylanthranilate isomerase cleaves the ribosyl ether bond to form o -carboxyphenylaminodeoxyribulose-5-phosphate. The molecular weight of the enzymes from Enterobacter hafniae, Aeromonas formicans and Proteus is 67 000. This is a key reaction step in the formation of tryptophan; the next step is the formation of indole-3-glycerol phosphate, which either forms tryptophan directly, or forms indole as an intermediate [A1481].

(—)-Epigallocatechin ether fission

(—)-Epigallocatechin ether fission

Musa accuminata forms 2-hydroxy-3-(2,4,6-trihydroxyphenyl)-1-(3,4,5-trihydroxyphenyl)-1-propanone from (—)-epigallocatechin; this presumably is an oxidative fission [K423].

3,4-Dihydroxyquinoline 2,4-dioxygenase

Arthrobacter and Pseudomonas putida enzymes form N-acetyl- and N-formylanthranilic acids, respectively, from 1H-3,4-dihydroxyquinaldine and 1H-3,4-dihydroxyquinoline, respectively, with release of carbon monoxide. Two oxygen atoms are incorporated, indicating oxygenolytic attack at C-2 and C-4 of both substrates [K774],

5,10-Methylenetetrahydrofolate dehydrogenase

(E.C. 1.5.1.5 and 1.5.1.15; NADP + and NAD + -requiring, respectively)

5,10-Methylenetetrahydrofolate 0 10-formyltetrahydrofolate

Pig liver enzyme appears to be a complex with 5,10-methenyltetrahydrofolate cyclohydrolase and 10-formyltetrahydrofolate synthetase (E.C. 6.3.4.3) [A2844].

In dihydrofolate-deficient immature domestic poultry chicks, activity is reduced by 25 per cent by folate or oestradiol, and these effects are additive [A1680].

Pisum sativum enzyme appears to be identical with 5,10-methenyltetrahydrofolate cyclohydrolase, but is separable from 10-formyltetrahydrofolate synthetase. Its molecular weight is 38 500, and it requires NADP [H619], with optimum pH 7.8 [A1429].

Saccharomyces cerevisiae enzyme is composed of two cytosolic isozymes; one requires NADPH and the other NADH [H794].

Peptostreptococcus productus 5,10-methylenetetrahydrofolate dehydrogenase, molecular weight 66 000 is a dimer. The product is said to be 5,10-methenyltetrahydrofolate, which makes it a different enzyme from others listed under this heading [F869].

5,10-Methylenetetrahydrofolate reductase

5,10-Methylenetetrahydrofolate 1 5-methyltetrahydrofolate.

Pig liver enzyme, molecular weight 77 300, contains one mol of FAD [C85].

Rat liver and brain enzymes are cytosolic, optimum pH 6.6 [A1586, A2502]. The reverse reaction requires FAD as hydrogen acceptor. An additional substrate for the reverse reaction is 5-methyltetrahydropteroylpentaglutamate [A2502].

Human platelet enzyme releases formaldehyde from 5-methyltetrahydrofolate [A2446].

Clostridium formicoaceticum enzyme is an octomer composed of two different monomers, molecular weights 26 000 and 35 000, and contains iron and zinc, acid-labile sulphur and FAD. It is inactivated by oxygen. For the reverse reaction, methylene blue, menadione, benzyl viologen or FAD can be used as oxidant [D260].

Peptostreptococcus productus enzyme is a dimer, molecular weight 66 000 [F869].

5,10-Methenyltetrafolate cyclohydrolase

Pisum sativum enzyme, molecular weight 38 500, which requires NADP, could not be separated from 5,10-methylenetetrafolate dehydrogenase (E.C. 1.5.1.5 and 1.5.1.15). It is inhibited by dihydrofolates [H619].

Pig liver enzyme is associated with a complex of enzymes that are involved with folate reactions [A2844].

Flavobacterium reversibly hydrolyzes a range of 5-aralkylhydantoins to N-carbamoylamino acids

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