Characteristics of Binding of a Potent Chemotactic Formyl Tetrapeptide, Formylmethionyl‐Leucyl‐Phenylalanyl‐Phenylalanine, to the Receptors on Rabbit Neutrophils

Binding of a potent chemotactic formyl tetrapeptide, formylmethionyl‐leucyl‐phenyl‐alanyl‐phenylalanine (fMet‐Leu‐Phe‐Phe), to the formyl peptide receptors on the rabbit neutrophil was assessed by two approaches. A tritiated preparation of fMet‐Leu‐Phe‐Phe was used for direct binding studies, whereas indirect studies comprised an assessment of the ability of the formyl tetrapeptide to competitively inhibit the binding of 35 S‐labeled formylmethionyl‐leucyl‐phenylalanine. These two approaches yielded analogous results. The formyl tetrapeptide fMet‐Leu‐Phe‐Phe showed rapid and saturable binding to the same chemotactic receptors as the less potent formyl tripeptides with which it was compared. Its equilibrium‐binding pattern, however, was different: fMet‐Leu‐Phe‐Phe showed a homogeneous binding pattern, in contrast to the heterogeneity seen with the less potent compounds. The relative potencies for high‐affinity binding of the two standard formyl tripeptides and fMet‐Leu‐Phe‐Phe correlated well with their relative potencies for stimulating the biological response of degranulation; the relative potencies for low‐affinity binding correlated less well.