3-Hydroxyanthranilate, from tryptophan

L-Tryptophan provides the anthranilate part of the molecule, most probably via a diversion of the classic pathway which forms 3-hydroxyanthranilate from L-tryptophan. Hydroxylation at C-8 of the antibiotic occurs prior to hydroxylation at C-7 and is accompanied by an NIH shift (27). The 8-methyl group of an-thramycin as well as the 7-methoxy carbon of 1 l-demethyltomaymycin are derived from methionine. 

Animals and yeasts can synthesize nicotinamide from tryptophan via hydroxyanthranilic acid (52) and quinolinic acid (53, Fig. 6A) (31), but the biosynthetic capacity of humans is limited. On a diet that is low in tryptophan, the combined contributions of endogenous synthesis and nutritional supply of precursors, such as nicotinic acid, nicotinamide, and nicotinamide riboside, may be insufficient, which results in cutaneous manifestation of niacin deficiency under the clinical picture of pellagra. Exogenous supply of nicotinamide riboside was shown to promote NAD+-dependent Sir2-function and to extend life-span in yeast without calorie restriction (32). 

Both anthranilic acid and hydroxyanthranilic acid can be formed from tryptophan in insect mutants, and both are conjugated with glycine to give substituted hippuric acids (796), whereas in plants or bacteria anthranilic acid tends to be conjugated as the /3-glucoside (848). 

Tryptophan is an essential amino acid involved in synthesis of several important compounds. Nicotinic acid (amide), a vitamin required in the synthesis of NAD+ and NADP+, can be synthesized from tryptophan (Figure 17-24). About 60 mg of tryptophan can give rise to 1 mg of nicotinamide. The synthesis begins with conversion of tryptophan to N-formylkynurenine by tryptophan pyrrolase, an inducible iron-porphyrin enzyme of liver. N-Formylkynurenine is converted to kynurenine by removal of formate, which enters the one-carbon pool. Kynurenine is hydroxylated to 3-hydroxykynurenine, which is converted to 3-hydroxyanthranilate, catalyzed by kynureninase, a pyridoxal phosphate-dependent enzyme. 3-Hydroxyanthranilate is then converted by a series of reactions to nicotinamide ribotide, the immedi-... 

The hypothetical pathway would lead from tryptophan to glutaric acid via 3-hydroxyanthranilic and cis-glutaconic acids. 

An unusual variant of a /8 elimination reaction is shown by kyneurinase which catalyses the production of L-alanine and 3-hydroxyanthranilate from 3-hydroxy kyneurine (Fig. 33), an intermediate in tryptophan biosynthesis. Although the reaction has not been subjected to mechanistic investigation a pathway consistent with the previously demonstrated properties of pyridoxal-P to stabilise a j8-carban-ion is illustrated in Fig. 34. 

The remaining atoms in anthramycin (166) can be identified with 4-methyl-3-hydroxyanthranilic acid (171), an intermediate in the biosynthesis of actinomycins from tryptophan.In accord, [7a- C]tryptophan was well incorporated into anthramycin. " ... 

Both tryptophan and tyrosine fiamished melanin. Similar results were also obtained by Allegri et al. (3), who studied melanin synthesis from tryptophan and tyrosine spectrophotometrically. From tyrosine, p-hydro-xyphenylpyruvic acid (15), 4,4-dihydroxybiphenyl (16), 5,6-dihydroxy-indole (17), and 3,5,6-trihydroxyindole (18) were obtained in addition to melanin and from tryptophan, 5,6-dihydroxyindole (17), indole (19), anthranilic acid (20), 3-hydroxyanthranilic acid (21), indolylpyruvic acid (22), 3-hydroxypyrrol-4,5-dicarboxylic acid (23), and isatin (24). 

Therefore, there is substantial evidence that 3-hydroxyanthranilic acid is an intermediate on the direct pathway of the synthesis of nicotinic acid from tryptophan. 

This conversion has been found to be catalyzed by an enzyme isolated from the liver and kidney of several mammalian species (6Jir67), from tryptophan-adapted Pseudomonas (68, 69), and from Neurospora (60). The enzyme appears to be identical with the system which causes the hydrolysis of 3-kynurenine to anthranilic acid. The products of the hydrolysis of hydroxykynurenine are hydroxyanthranilic acid and alanine. Pyri-doxal phosphate is required for the reaction. 

Synthesis of 4-methyl-3-hydroxyanthranilic acid from tryptophan... 

Alkaloids derived from nicotinic acid contain a pyridine nucleus. Nicotinic acid itself is synthesized from L-tryptophan via A-formylkynurenine, L-kynurenine, 3-hydroxykynurenine, 3-hydroxyanthranilic acid and quinolinic acid. 

Figure 20.21 Catabolism of tryptophan by the serotonin and 3-hydroxyanthranilate pathways. B, B2, and B6 indicate the participation of coenzymes derived from the respective vitamins. Notice that tryptophan is glucogenic and ketogenic, because it produces alanine on the one hand, and acetoacetyl-CoA on the other.

It was furthermore reported (K20) that nicotinic acid-deficient animals would grow only if given tryptophan, thus suggesting the conversion of tryptophan to nicotinic acid. Not only is tryptophan converted to nicotinic acid but also kynurenine and 3-hydroxyanthranilic acid. The peculiar degradation of the latter to pyridine derivatives gave rise to many interesting investigations. 3-Hydroxyanthranilic acid is derived from 3-hydroxykynurenine, another important tryptophan metabolite, the his-... 

From our investigation it is evident that abnormal excretion of tryptophan metabolites is not a typical feature of bladder tumor subjects, since human beings with neoplastic and nonneoplastic extrabladder urinary diseases have also been found to excrete spontaneously elevated amounts of tryptophan derivatives. It seems that the metabolic abnormality is not restricted to bladder tumors, but is rather more specific for patients with tumors of the upper urinary tracts and of the renal parenchyma. Actually 59% of these patients (Fig. 4) excreted abnormal amounts of kynurenine, 3-hydroxykynurenine, and 3-hydroxyanthranilic acid. 

Isotopic experiments (763) with tryptophan labeled with N and deuterium in the indole ring have shown that quinolinic acid nitrogen is probably entirely derived from the indole nitrogen of tryptophan, and that scission of the benzene ring probably occurs between carbons 3 and 4. Presumably, therefore, the hydroxyanthranilic acid is converted to intermediate A without participation of a catechol-type intermediate, and it is possible that the phosphate-bond energy of hydroxyanthranilic acid phosphate (if this is in fact an intermediate) may contribute to the transformation. It is known... 

Tryptophan catabolism. The major pathway of tryptophan catabolism is presented above. The early steps are shown in detail, with the formation of niacin and acetyl CoA from 3-hydroxyanthranilate shown with no detail. 

BiosytMesis In animals tryptophan - kynutenine - 3-hydroxyanthranilic acid - quinolinic acid (pyri-dine-2,3-dicaiboxylic acid) - nicotinic acid - nicotinamide. In bacteria and higher plants from L- aspar-tic acid and a C3-unit, probably D-glyceraldehyde 3-phosphate. Also by cleavage of NAD. 

Degradation of L-tryptophan in most organisms proceeds via L-kynurenine, 3-hydroxy-L-kynurenine, 3-hydroxyanthranilic acid and quinolinic acid to acetyl Co A and CO2 (Fig. 244). Anthranilic acid formed as an intermediate may be recycled to L-tryptophan (see above). The ring of 3-hydroxyanthranilic acid is cleaved by a dioxygenase (C 2.5). The x-amino-/3-carboxymuconic acid-e-semialdehyde formed either undergoes a cis trans isomerization of the Zl -double bond and cyclization to quinolinic acid, a compound synthesized in microorganisms and plants from aspartic acid and D-glyceraldehyde-3-phosphate (D 16.2). On the other hand o -amino-/3-carboxymuconic acid-e-aldehyde may be de-carboxylated and is then the immediate precursor of NH3, acetic acid and COg. 

Quinolinic Acid. Assignment of a place to quinolinic acid as an intermediate in nicotinic acid formation is based on the evidence that its excretion into the urine is increased by injection of tryptophan or of 3-hydroxyanthranilic acid. Quinolinic acid isolated from the urine on treatment with acid gives rise to a substance having niacin activity for L. arabinosus. ... 

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... 

A further important pathway of L-tryptophan metabolism also diverges from 2-amino-3-carboxy-m, cis muconic semi-aldehyde (26) the ring fission product of 3-hydroxyanthranilate (25) and this is the biosynthetic pathway which leads to the formation of the pyridine ring of the nicotinamide nucleotides . The first step in this pathway appears to be the recyclisation of the oxidation product (26) to give quinolinic add (27) which is transformed to the pyridine nucleotides, such as NAD (28) in a complex series of reactions. Figure 4.6. 

Y. Nishizuka, A. Ichiyama, R. K. Gholson, and O. Hayaishi, Studies on the metabolism of the benzene ring of tryptophan in mammalian tissues. I. Enzymic formation of glutaric acid from 3-hydroxyanthranilic acid, / Biol. Chem. 240, 733-739 (1965). 

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