3-Hydroxyanthranilic acid oxidase

In 1961, Priest el al. (6S) found that kidney and liver contiuned a soluble enzyme system which could promote the oxidation of 3-hydroxyanthranilic acid to quinolmic acid. Bokman and Schweigert (64) were able to demonstrate that an intermediate was involved in the oxidation. This intermediate can be characterized by an absorption maximum at 360 laix and has been referred to as compound 1, which spontaneously decomposes to quinolinic acid (66-67). Oxygen and ferrous ion are required for the formation of the intermediate (67), but not for its quantitative conversion to quinolinic acid. Compoimd I has been established by Wiss and Bettendorf (68) to be l-amino-4-formyl-l,3-butadiene-l,2-dicarboxylic acid. The enzyme 3-hydroxyanthranilic acid oxidase from beef liver has been purified slightly and evidence for the requirement of ferrous ion and sulfhydryl groups for activity has been obtained (68a). 

SS4). The intermediate can be converted quantitatively to quinolinic acid by heating at 100 and nearly complete conversion is obtained on incubation of hydroxyanthranilate with liver slices or high concentration of hydroxyanthranilic acid oxidase. 

In independent studies, Aprison et al. (A7) found among tryptophan metabolites that 3-hydroxyanthranilic acid was capable of inhibiting the oxidation of N,N-dimethyl-p-phenylendiamine by purified ceruloplasmin and serum oxidase. 

Figure 2 NAD metabolism. Tip = tryptophan, 3-HK = 3-hydroxykynurenine, 3-HA = 3-hydroxyanthranilic acid, ACMS = a-amino-P-carboxymuconate- -semialdehyde, AMS = a-aminomuconate- -semialdehyde, NaMN = nicotinic acid mononucleotide, NMN = nicotinamide mononucleotide, NaAD = nicotinic acid adenine dinucleotide. For other abbreviations, see Figure 1. (1) tryptophan oxygenase [EC 1.13.11.11], (2) formy-dase [EC 3.5.1.9], (3) kynurenine 3-hydroxylase [EC 1.14.13.9], (4) kynureninase [EC 3.7.1.3], (5) 3-hydroxyanthranilic acid oxygenase [EC 1.13.11.6], (6) nonenzymatic, (7) aminocarboxymuconate-semialdehyde decarboxylase [EC 4.1.1.45], (8) quinolinate phos-phoribosyltransferase [EC 2.4.2.19], (9) NaMN adenylyltransferase [EC 2.7.2.18], (10) NAD synthetase [EC 6.3.5.1], (11) NAD kinase [EC 2.7.1.23], (12) NAD" glycohydro-lase [EC 3.2.2.5], (13) nicotinamide methyltransferase [EC 2.2.1.1], (14) 2-Py-forming MNA oxidase [EC 1.2.3.1], (15) 4-Py-forming MNA oxidase [EC number not given], (16) nicotinamide phosphoribosyltransferase [EC 2.4.2.12], (17) NMN adenylytransferase [EC 2.7.71], (18) nicotinate phosphoribosyltransferase [EC 2.4.2.11], (19) nicotinate methyltransferase [EC 2.7.1.7], and nicotinamidase [EC 3.5.1.19]. Solid line, biosynthesis dotted line, catabolism.

Several alternative pathways of L-tryptophan metabolism diverge from kynurenine (24). In mammals the quantitatively major fate of the benzene ring of the amino acid appears to be its oxidation to carbon dioxide via 3-hydroxyanthranilic acid (25), Figure 4.5. Kynurenine is first hydroxylated by a typical mixed function oxidase and the side chain is then removed, under the... 

Hydroxyanthranilate oxidase functions during intermediary metabolism of tiyptophan, as depicted in Figure 4. It transforms 3-hydroxyanthranilic acid into a substance, not raitirely characterized, from which quinolinic, picolinic, and nicotinic adds arise (75,76, 188,346,348,449,540,649,650,776,833, and the reviews 182,312,538). The enzyme occurs in pig, ox and rat liver and kidney, but not in other organs (348,600,650,666). 

Tracer studies of the fate of oxygen consumed during protocate-chuic acid cleavage have not been carried ocit, but because of oxygen stoichiometry, dependence of the enzyme upon ferrous ions, and resemblance of the over-all reaction to those catalyzed by pyrocate-chase, homogentisate oxidase, and 3-hydroxyanthranilate oxidase (compare 171), it is reasonable to classify protocatechuic acid oxidase as an oxygen transferase. 

Figure 8.4. Pathways of tryptophan metaholism. Tryptophan dioxygenase, EC 1.13.11.11 formylkynurenine formamidase, EC 3.5.1.9 kynurenine hydroxylase, EC 1.14.13.9 kynureninase, EC 3.7.1.3 3-hydroxyanthranilate oxidase, EC 1.10.3.5 picolinate carboxylase, EC 4.1.1.45 kynurenine oxoglutarate aminotransferase, EC 2.6.1.7 kynurenine glyoxylate aminotransferase, 2.6.1.63 tryptophan hydroxylase, EC 1.14.16.4 and 5-hydroxytryptophan decarboxylase, EC 4.1.1.26. Relative molecular masses (Mr) tryptophan, 204.2 serotonin, 176.2 kynurenine, 208.2 3-hydroxykynurenine, 223.2 kynurenic acid, 189.2 xanthurenic acid, 205.2 and quinolinic acid 167.1. CoA, coenzyme A.

Indirect evidence for the existence of such an enzyme arose from the observation [30] that in vitro administration of anthranilic acid to rat neurons causes an increase in intracellular HA concentration. However, that study did not pay due attention to the earlier observation [31], that anthranilic acid is an effective inhibitor (Ki 40 pM) of the enzyme, devoted to HA oxidation, 3-hydroxyanthranilate oxidase (dioxygenase). Therefore, the increase in HA concentration could well be due to an inhibitory effect of anthranilic acid towards the further catabolism of HA, and not to a direct conversion of anthranilic acid to HA. 

An enzyme catalyzing the oxidation of 3-hydroxyan-thranilic acid was found in liver and kidney. The 3-hydroxyanthranilic oxidase has been partially purified from beef liver, and requirements for ferrous ions and sulfhydryl groups have been demonstrated. 

In the presence of O2, the oxidase opens the ring of 3-hydroxyanthranilate and oxidizes both the carbon bound to the hydroxyl group to yield a carboxyl group and the adjacent carbon to yield an aldehyde group. 2-Acroleyl-3-aminofumarate is the final product of the reaction. The nitrogen is then incorporated into a heterocyclic ring of quinolinic acid (or pyridine-2,3-... 

S-Hydroxyanthranilic Oxidase. In animals an oxidation of 3-hydroxy-anthranilic acid by an oxidase from liver is known, but it is not known that other reactions do not occur. The oxidase, a soluble enzyme that survives acetone drying, consumes one equivalent of O2 in forming an unstable product believed to have the structure shown in (XI).This... 

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