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When considering the catabolism of IAA, the following well-known chemical reactions of indoles and 3-substituted indoles have to be considered: (i) oxidations that alter the side chain, (ii) oxidations resulting in production of oxindole or dioxindole compounds, (iii) opening of the pyrrole ring and further reactions, and (iv) conjugation with, for example, amino acids, carbohydrates, or other small molecules. Reactions of types i, ii, and iv have been characterized in bacteria (6, 12, 15), plants (13, 17, 18, 20, 21), and plant tissues (2, 14). Reactions of type iii, opening of the pyrrole ring and further reactions, have only been described for bacteria, e.g., Arthrobacter spp. (15), Pseudomonas spp., (19), and "a micro-organism isolated from air" (23).

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By monitoring IAA degradation by UV absorption, we see that the characteristic spectrum from the indole ring disappears. Splitting of the indole ring has been described for bacteria only. For Pseudomonas spp., it has been suggested that IAA is catabolized by modifications of the side chain followed by a hydrolytic opening of the pyrrole ring. Salicylic acid and catechol have been identified as degradation products (19). In Arthrobacter spp., catechol and pyrogallol have been identified as degradation products (15). For "a micro-organism isolated from air" (23), it has been suggested that IAA is degraded by an oxidative opening of the indole ring in a reaction analogous to the one catalyzed by tryptophan 2,3-dioxygenase. o-Formaminobenzoyl-acetic acid and anthranilic acid have been identified as degradation products.

(L.A. Egebo, S.V.S. Nielsen, B.U. Jochimsen - 1991)

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..On the other hand, many investigaters have been interested in the plant hormone, indole-3-acetic acid, which is formed from Try has shown that a species of Arthrobacter, which was isolated from the air, can utilize indole-3-acetic acid and L-tryptophan as its sole source of carbon and nitrogen. This paper describes a new scheme of complete oxidation of Try through IAA by this bacterium.

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