INTERACTION OF AUXIN-BINDING PROTEIN-1 WITH MAIZE COLEOPTILE PLASMA-MEMBRANES IN-VITRO

In a search for membrane ''docking proteins'' interacting with Zea may s auxin-binding protein (ABP1) the binding of purified ABP1 to maize c oleoptile plasmamembrane vesicles was investigated. Concentration-depe ndent, saturable binding of ABP1 to the membrane vesicles was observed in binding assays using 10(-8)- 10(-6) M ABP1. Biotinylated ABP1 was displaced from the membrane binding sites by competition with unlabele d ABP1, demonstrating specific binding. The association step proved to be pH-dependent with maximum binding at pH 5.0 or lower. Auxins did n ot influence the ABP1 binding to plasma-membrane vesicles, but ABP1 as sociated with plasma-membrane vesicles was still able to specifically bind [H-3]naphthalene-l-acetic acid. The rather stable interaction of ABP1 with plasma-membrane vesicles was only affected by strong alkalin e buffers or detergents. The binding capacity was calculated to be in the range of 0.2 pmol ABP1 per g coleoptile fresh weight.