Rigin, another phagocytosis-stimulating tetrapeptide isolated from human IgG. Confirmations of a hypothesis.

Structure-function and conformational studies of the molecule of phagocytosis-stimulating tetrapeptide tuftsin permitted the conclusion that among products resulting from splitting of H-chain of IgG Human EU by trypsin, besides tuftsin (sequence 289-292), tuftsin-like tetrapeptide Gly-Gln-Pro-Arg may be also present; theoretical conformational analysis shows a considerable similarity of spatial arrangement of this tetrapeptide and tuftsin which testifies in favour of potential tuftsin-like activity of the tetrapeptide. Gly-Gln-Pro-Arg was synthesized and its phagocytosis stimulating activity was found equal to that of tuftsin.