Identification of a high affinity binding site for lipo-oligosaccharidic NodRm factors in the microsomal fraction of Medicago cell suspension cultures

Protease-sensitive binding sites for a S-35-labeled ligand corresponding to the major lipo-oligosaccharidic symbiotic signal of Rhizobium meliloti (NodRm factor), have! been identified in the microsomal fraction of Medicago varia cell suspension culture extracts. Binding was reversible and saturable and tetra-N-acetyl chitotetraose was a poor competitor of NodRm binding. Scatchard analysis suggests the presence of a high affinity binding site, termed Nod factor binding site two (NFBS2), with a K-d of 1.9 nM, and perhaps a second site with an affinity (K-d of 70 nM) similar to that of a site (NFBS1) previously characterized in Medicago truncatula root extracts.