A SOLUBLE HIGH-AFFINITY AUXIN-BINDING PROTEIN FROM PEA APEX

A soluble auxin-binding protein (ABP(44)) from etiolated seedlings of Pisum sativum L. has been purified. It was detected in the apex but no t in the basal, non-dividing pans of the pea epicotyls. Different set- ups of affinity chromatography were found to be powerful tools for the purification and characterization of ABP(44). The determination of th e binding kinetics was done using equilibrium dialysis binding tests. The modifications and improvements of the equilibrium binding assay, d escribed previously (Reinard and Jacobsen, 1989), allowed the assignme nt of auxin binding activity to a purified soluble protein (ABP(44)) w ith a dissociation constant of K-D = 7.5 nM for the naturally occurrin g IAA. The data presented indicate that ABP(44) binds active auxins bo th with a high affinity and great specificity.