Characterization of fusicoccin binding to receptor sites on cell membranes of maize coleoptile tissues

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Abstract
Radioactive dihydrofusicoccin (3H‐FC), known to have the same biological activity as fusicoccin on plant tissues, has a specific affinity in vitro for sites localized on subcellular, postmitochondrial particles from maize coleoptiles. The analysis of the kinetics of dihydrofusicoccin binding suggests the presence of two classes of sites, one class with a high affinity and a second class with a lower affinity. The high affinity class of sites has a dissociation constant (Kd) of 1.2 × 10−9 mol dm−3, and an apparent pH optimum at 5.5. Binding is antagonized by non‐physiological pH, high temperatures and protein‐reactive substances like HgCl2, p‐chloromercuribenzensulphonate and glutaraldehyde. Treatment of dihydrofusicoccin‐bound membrane preparations with Triton X‐100 leads to the solubilization of a protein fraction associated with dihydrofusicoccin. These data suggest a protein nature for the receptor sites.