Plant Physiology 66:1074-1078 (1980)
© 1980 American Society of Plant Biologists
Articles
Solubilization of the Receptor for N-1-Naphthylphthalamic Acid 1
Michael R. Sussman2 and
Gary Gardner
Shell Development Company, Biological Sciences Research Center, P.O. Box 4248, Modesto, California 95352
A receptor protein for the auxin transport inhibitor, N-1-naphthylphthalamic acid (NPA), has been solubilized from corn coleoptile membranes using Triton X-100. [3H]NPA binding activity of the receptor was compared in soluble and membrane-bound states. Both activities are abolished by treatment with trypsin. Differences between the two are observed in pH optima and rates of heat inactivation.
At pH 5, the membrane-bound and solubilized receptors have similar affinity for NPA (Kd about 107 molar). Solubilization results in a 10-fold increase in affinity for the low-affinity auxin analogs, - and -naphthaleneacetic acid (Kd about 105 molar). There is no measurable competition by indoleacetic acid (Kd > 103 molar) for [3H]NPA binding to membranes, but there is competition with the solubilized receptor (Kd for IAA about 105 molar). There is no measurable competition with benzoic acid in either preparation. These observations of an affinity of auxin analogs for the solubilized NPA receptor raise the interesting possibility that the NPA binding site is one conformation of an auxin binding site involved in polar auxin transport.
2 Present address: Department of Human Genetics, Yale University Medical School, 333 Cedar St., New Haven, CT 06510.
1 Preparation of this manuscript was supported in part by National Science Foundation Grant PCM-73-01089.
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