Auxin binding to corn coleoptile membranes: Kinetics and specificity

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Abstract
Detailed examination of binding over the range 10-7–10-6 M suggests that membrane preparations from coleoptiles of Zea mays L., cv Kelvedon 33 contain at least two sets of high affinity binding sites for 1-naphthylacetic acid (NAA), with dissociation constants of 1.8×10-7 M (site 1) and 14.5×10-7 M (site 2). Similar studies with 3-indolylacetic acid (IAA) also indicate two sets of binding sites, whose concentrations are closely comparable to those deduced for NAA. A substantial proportion of the total binding activity is retained in a detergent-solubilized preparation. Using [14C]NAA the interactions of a range of analogues with each of the binding sites have been examined with the aid of double reciprocal plots. The specificity of site 2 is compatible with that expected for an auxin receptor, in that only active auxins, antiauxin transport inhibitors are able to compete with [14C]NAA for the binding sites. Site 1 on the other hand is less specific, since it appears to bind all compounds tested, including physiologically inactive analogues.