Sukekatsu Nozaki

Phagocytosis-Stimulating Activity of Tuftsin Analogs

Najjar and his associates showed that a specific cell bound leucophilic y-globulin fraction, leucokinin, is essential for maximal stimulation of the phagocytic activity of the blood neutrophilic leucocyte (1, 2). Soon thereafter it was found that the whole stimulatory effect of leucokinin can be ascribed to a single peptide fragment liberated from leucokinin by a specific enzyme, leucokininase (3, 4). This natural phagocytosis-stimulating peptide has been referred to as tuftsin (5), and its primary structure has been determined to be H-Thr-Lys-Pro-Arg-OH (3). Studies of synthetic analogs have revealed that the removal of N-terminal threonine or C-terminal arginine leads to nullification of the activity of the peptide and the addition of proline to the tuftsin sequence, that is, H-Thr-Lys-Pro-Pro-Arg-OH, also decimates the biological