Neokyotorphin and neokyotorphin (1-4): secretion by erythrocytes and regulation of tumor cell growth.

Human erythrocytes release neokyotorphin, the 137-141 fragment of hemoglobin alpha-chain into the supernatant of red blood cells primary culture. However, the neokyotorphin fragment 1-4 that is formed together with neokyotorphin inside the red blood cells and in various tissues is not found in the supernatant. Both neokyotorphin and its 1-4 fragment were shown to stimulate proliferation of L929 tumor cells.