Azido Auxins

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Abstract
The binding constants of three auxin analogs, 4-, 5-, and 6-azidoindole-3-acetic acid (4-, 5-, and 6-N3IAA), and of the photoproducts of 5-N3IAA to the naphthalene-1-acetic acid (NAA) binding sites of Zea mays L. WF9 × BR38 were determined to evaluate the potential of these analogs as photoaffinity labeling agents. We have found that 4- and 5-N3IAA bind to these sites with affinities similar to that of IAA, while 6-N3IAA and the photoproducts of 5-N3IAA bind less tightly. This binding is fully reversible in the dark. Binding of 5-N3IAA becomes covalent and irreversible upon UV irradiation, as evidenced by a 30% loss in NAA binding at sites pretreated with 5-N3IAA and UV irradiation, then washed extensively. IAA or NAA, included with this 5-N3IAA pretreatment, can protect the sites from blockage, whereas benzoic acid and tryptophan are unable to protect the site, indicating that 5-N3IAA specifically labels the auxin sites.
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