If an enzyme name is shown in bold, there is experimental evidence for this enzymatic activity.
|Superclasses:||Degradation/Utilization/Assimilation → Amino Acids Degradation → Tryptophan Degradation|
Expected Taxonomic Range: Proteobacteria
Tryptophan is initially oxidized by L-tryptophan:oxygen 2-oxidoreductase (side-chain-cleaving), also called indole acetaldehyde:oxygen 2-oxidoreductase or TSO, to indole acetaldehyde and then indole-3-glycol aldehyde. The later can be further oxidized by the same enzyme to indole-3-glyoxal. Thus, three different indole aldehydes are formed from tryptophan. Next, each of the three indole aldehydes undergoes further oxidation or reduction to the corresponding indole acid or alcohol, by the action of aldehyde dehydrogenase and alcohol dehydrogenase, respectively. This results in the acids indole-3-acetate, indole-3-glycolate, and indole-3-glyoxylate, and the alcohols indole-3-ethanol, indole-3-glycol and indole-3-ketol.
Finally, TSO oxidizes indole-3-acetate to indole-3-glycolate, and indole-3-ethanol to indole-3-glycol, and further oxidizes these two intermediates to the final products, indole-3-glyoxylate and indole-3-ketol.
Thus, the side chain pathway is initiated by the formation of indole-3-acetaldehyde or indole-3-glycolaldehyde from L-tryptophan by TSO, and continues by three types of oxidoreduction modifications of the side chain; namely the consecutive oxidation at the α- carbon of the side chain by TSO, and the reduction and oxidation of the indole aldehydes to the corresponding indole alcohols and acids, as catalyzed by alcohol dehydrogenase and aldehyde dehydrogenase , respectively [Narumiya79].
This pathway coexists in P. fluorescens with the anthranilate pathway (tryptophan degradation I (via anthranilate)) [Oberhansli91]. The anthranilate pathway is active during exponential growth, while the side-chain oxidase pathway is induced in stationary phase [Narumiya79]. In addition, the side-chane oxidase pathway is preferred under acidic growth conditions, while the anthranilate pathway is preferred during more alkaline conditions [Oberhansli91].
Variants: tryptophan degradation I (via anthranilate) , tryptophan degradation II (via pyruvate) , tryptophan degradation III (eukaryotic) , tryptophan degradation IV (via indole-3-lactate) , tryptophan degradation to 2-amino-3-carboxymuconate semialdehyde , tryptophan degradation VI (via tryptamine) , tryptophan degradation VII (via indole-3-pyruvate) , tryptophan degradation VIII (to tryptophol) , tryptophan degradation IX , tryptophan degradation X (mammalian, via tryptamine) , tryptophan degradation XI (mammalian, via kynurenine) , tryptophan degradation XII (Geobacillus)
Narumiya79: Narumiya S, Takai K, Tokuyama T, Noda Y, Ushiro H, Hayaishi O (1979). "A new metabolic pathway of tryptophan initiated by tryptophan side chain oxidase." J Biol Chem 254(15);7007-15. PMID: 110802
Oberhansli91: Oberhansli T, Dfago G, Haas D (1991). "Indole-3-acetic acid (IAA) synthesis in the biocontrol strain CHA0 of Pseudomonas fluorescens: role of tryptophan side chain oxidase." J Gen Microbiol 137(10);2273-9. PMID: 1663150
Roberts77a: Roberts J, Rosenfeld HJ (1977). "Isolation, crystallization, and properties of indolyl-3-alkane alpha-hydroxylase. A novel tryptophan-metabolizing enzyme." J Biol Chem 252(8);2640-7. PMID: 15994
Takai77: Takai K, Ushiro H, Noda Y, Narumiya S, Tokuyama T (1977). "Crystalline hemoprotein from Pseudomonas that catalyzes oxidation of side chain of tryptophan and other indole derivatives." J Biol Chem 252(8);2648-56. PMID: 15995
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