Evaluation of the C‐terminal C5a effector site with short synthetic C5a analog peptides

Biological activities have been determined for a series of 18 peptides based on the C‐terminal sequence of human or rat C5a. Lysosomal enzyme release was tested in two cell types, the promyelotic leukemia cell line U937 and polymorphonuclear leukocytes. In addition, an ATP‐release assay with guinea pig platelets was performed. It was demonstrated that the C‐terminal octapeptide 67‐74 of human C5a represents the minimal sequence required to induce a measurable biological signal in all assays. Extending this peptide to a length of 21 amino acids produced at best only a slight enhancement of potency. Amino acid replacements with either tryptophanyl or phenylalanyl residues in positions between 65–69 either increased potency (at position 67), or abrogated potency (at position 66) in the two lysosomal enzyme assays. N‐terminal acylation with the fluorenylmethoxy‐carbonyl‐aminohexanoyl group slightly enhanced C5a potency. In desensitization experiments with guinea pig platelets all peptides with a C5a activity were able to desensitize not only the C5a but also the C3a responses.