title: Photoaffinity labeling of soluble auxin-binding proteins.
abstract: The photoaffinity labeling agent azido-IAA (5-N3-[7-3H]indole-3-acetic acid), a biologically active analogue of the endogenous auxin indole-3-acetic acid, was used to search for auxin-binding proteins in the soluble fraction of Hyoscyamus muticus cells. Azido-IAA became covalently attached to three polypeptides with a high specific activity. The labeling was specific for IAA and not due to random tagging. Two polypeptides with molecular masses of 31 and 24 kDa in the 0-30% ammonium sulfate fraction were labeled after UV photolysis at 0 degree C but not at -196 degrees C, and appeared to have a high affinity indole-binding site(s) for which active, non-indole auxins were not good ligands. A third polypeptide with a molecular mass of 25 kDa present in the 50-60% ammonium sulfate fraction labeled exclusively at -196 degrees C and had a significant affinity for active auxins but not for inactive indoles. The azido-IAA labeling pattern, pI, competition results, and immunoprecipitation all indicate that the 31- and 24-kDa polypeptides are related to the basic form of endo-1,3-beta-glucanase (EC 3.2.1.39). Azido-IAA labeling polypeptides equivalent to the 31- and 24-kDa species were apparently also present in the cell wall. The low pH optimum for binding of azido-IAA to the 25-kDa polypeptide suggests the location of the active protein in a compartment such as the vacuole or a transport vesicle rather than in the cytosol.
authors.affiliation: Friedrich Miescher-Institut, Basel, Switzerland.
authors.forename: H
authors.initials: H
authors.lastname: Macdonald
authors.forename: A M
authors.initials: AM
authors.lastname: Jones
authors.forename: P J
authors.initials: PJ
authors.lastname: King
mesh_terms: D000345:Affinity Labels; D001386:Azides / Q000737:chemistry; D002478:Cells, Cultured; D004591:Electrophoresis, Polyacrylamide Gel; D006868:Hydrolysis; D007210:Indoleacetic Acids / Q000737:chemistry / Q000378:metabolism*; D010777:Photochemistry; D010937:Plant Growth Regulators; D010940:Plant Proteins; D010944:Plants / Q000378:metabolism*; D011956:Receptors, Cell Surface / Q000737:chemistry*
chemical_list: D000345:Affinity Labels; D001386:Azides; D007210:Indoleacetic Acids; D010937:Plant Growth Regulators; D010940:Plant Proteins; D011956:Receptors, Cell Surface; C046131:auxin receptor, plant; C068520:5-azido-1H-indole-3-acetic acid