HIGH-AFFINITY BINDING OF A PROTEIN-LIPOPOLYSACCHARIDE PHYTOTOXIN FROMVERTICILLIUM-DAHLIAE TO COTTON MEMBRANES

The presence of a specific binding site for a protein-lipopolysacchari de (PLP) phytotoxin isolated from culture filtrates of Verticillium da hliae has been demonstrated in plasma membranes from cotton seedlings. The I-125-labelled PLP was used as a ligand in binding assays with pl asma membrane enriched fractions. Root tissue exhibited the highest am ount of binding activity compared to hypocotyl and cotyledon tissue. B inding of the [I-125]PLP was saturable, reversible, and with an affini ty (K-d = 1.42 X 10(-8)M) comparable with the concentration required f or biological activity. A single class of binding site was found, and the maximal number of binding sites were estimated as 5.4 x 10(-15) mo l/mu g protein.