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Articles

Azido Auxins

Quantitative Binding Data in Maize ¹

Department of Plant Biology and School of Chemical Sciences, University of Illinois, Urbana, Illinois 61801

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 x 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.

³ School of Chemical Sciences.

¹ Supported by grants from the National Science Foundation (PCM 77-14175 and PCM 80-21632), Hoffman-LaRoche Foundation, and the Graduate Research Board, University of Illinois, and by a Dissertation Grant to A. M. J. Presented, in part, at the 11th International Conference on Plant Growth Substances, Aberystwith, Wales, July 10-16, 1982.

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