title: The binding of the B-chain of ricin to Burkitt lymphoma cells. A new approach to ligand-receptor interaction studies.
abstract: It is shown that conformational changes of receptor proteins brought about by binding of a ligand induce changes in the lipid environment of the receptor that can be monitored by fluorescent lipid probes. On this basis a new approach to studies of ligand-receptor binding is proposed. Using the interaction of the ricin B-chain with Burkitt lymphoma cells as an example and fluorescent labelled sphingomyelin as a probe, the ligand-induced changes of fluorescence anisotropy were shown to be concentration-dependent and to permit determination of the binding constant and the number of receptor-binding sites. The method was found to be specific and highly sensitive, allowing detection of the action of one RB molecule per cell. Scatchard analysis of the binding of 125I-RB demonstrated the presence on the cell surface of two binding sites with Kd approximately 10(-10) and approximately 10(-8) M, respectively. Only the high-affinity sites were detected by the fluorescence technique. Saturation of these sites resulted in maximum inhibition of protein synthesis.
mesh_terms: D002051:Burkitt Lymphoma / Q000378:metabolism*; D002460:Cell Line; D005454:Fluorescence Polarization; D005456:Fluorescent Dyes; D006801:Humans; D007700:Kinetics; D009363:Neoplasm Proteins / Q000378:metabolism*; D011485:Protein Binding; D011869:Radioligand Assay; D011975:Receptors, Mitogen / Q000032:analysis* / Q000187:drug effects; D012276:Ricin / Q000378:metabolism* / Q000494:pharmacology; D013229:Stearic Acids
chemical_list: D005456:Fluorescent Dyes; D009363:Neoplasm Proteins; D011975:Receptors, Mitogen; C032650:Ricinus communis lectin receptor; D013229:Stearic Acids; D012276:Ricin