Pseudo-Enzymatic Properties of Haptoglobin:Hemoglobin Complexes | Biomedgrid

Hemoglobin (Hb) and free heme are physiologically released into human plasma upon hemolysis of senescent erythrocytes and erythroblasts enucleation, and pathologically because of severe hematologic diseases and blood transfusion. To inhibit the heme-based formation of free radicals, several plasma proteins have been evolved. In particular, haptoglobin (Hp) binds αβ dimers of Hb allowing the Hb removal via the reticuloendothelial system and the CD163 receptor-mediated endocytosis in hepatocytes, Kupffer cells, and tissue macrophages. In turn, the Hp:Hb complexes facilitate heme-based detoxification of NO and peroxynitrite and display NO2 ‒ reductase activity opening new avenues in removing reactive nitrogen species in plasma. The correlation between Hp glycosylation, the stability of the Hp:Hb complexes and pathological conditions (i.e., cancer) has been observed