• chemotaxis;
  • chemotactic selection;
  • bradykinin;
  • Tetrahymena;
  • phylogeny

The chemotactic character of the nonapeptide bradykinin (BK1–9) and its derivatives was studied in the eukaryotic ciliated model Tetrahymena pyriformis. The results demonstrate that BK1–9 has a direct and ligand-specific chemoattractant effect (maximal at 10−11m) without any intermediate substance as is essential in some mammalian test systems. Evaluation of the chemotactic effect elicited by derivatives showed that the presence of N- and C-terminal arginines can influence chemotactic potency of the molecule via expression of pyrrolidine and aromatic ring structures of terminal amino acid residues. Removal of the N-terminal Arg (expression of Pro) results in a significant decrease in chemotaxis (BK2–9), while further truncation of the C-terminal, causing expression of the aromatic ring of Phe (BK2–8), results in a highly chemoattractant variant. A single pyrrolidine ring on the C-terminus BK1–7 also has a positive effect on the chemotactic character, however further truncation (BK1–6, BK1–5) causes the chemoattractant character to become chemorepellent. Study of chemotactic selection with BK derivatives supports our previous findings that only phylogenetically selected ligands or their close derivatives are able to induce long-term selection with chemotaxis.