Heterogeneity of Binding of Chemotactic Formyl Peptides to their Receptors on Rabbit Neutrophils: Methodological and Analytical Considerations in the Study of Complex Receptor-Binding Patterns

Abstract

The pattern of binding of chemotactic formyl peptides to their receptors on intact rabbit neutrophils was investigated using three different radiolabeled formyl peptides. The purpose of the study was both to establish suitable procedures for the analysis of complex receptor-binding data and to evaluate the heterogeneity of binding of the chemotactic formyl peptides. Radiolabeled formylmethionyl-leucyl-phenylalanine was found to require repurification by thin-layer chromatography before it was of sufficient purity for use in these studies. All three radioligands were essentially stable during the binding assay. The ‘LIGAND’ computer program proved suitable for a detailed and rigorous analysis of the binding data. Each of the three formyl peptides showed significant heterogeneity in its binding pattern and all appeared to interact with the same receptor sites. The degree of heterogeneity, however, was greater with formylnorleucyl-leucyl-phenylalanine than with the other two formyl peptides. The heterogeneity was close to the theoretical limit of discernibility; thus individual binding studies with one formyl peptide did not always show statistical evidence of the heterogeneity. The study also highlighted the severe uncertainty in estimates of the proportions of each type of binding site when such data are analyzed on the basis of the ‘two binding site’ model.