Napthaleneacetic acid binding by membrane-free preparations of cytosol from the maize coleoptile

Abstract

Maize cytosol preparations have been shown to contain compounds which are capable of binding napthalene-1-acetic acid (NAA). These compounds were fractionated by Sephadex G-100 chromatography into several different binding components. Approximately 70% of the total binding activity was associated with a compound, presumed to be proteinaceous, of molecular weight of 38 700. It had an NAA dissociation constant of 3.6 × 10⁻⁶ M with a site concentration of 160 pmol/g fresh wt. Hydroxylapatite and diethylaminoethyl (DEAE)-Sephacel chromatography indicated that the principal Sephadex fraction was heterogenous. A number of auxins and structurally related compounds were tested for their ability to inhibit NAA binding by cytosol or membrane preparations. A better correlation between the growth promoting effects of these compounds and their ability to inhibit NAA binding was found using cytosol, as compared with membrane preparations.