Lactoferrin is widely distributed in human and mammalian milk and various other tissues and their secretions (including tears, semen, bile, synovial fluid, and other internal and external secretions, as well as neutrophils), but its content is higher in milk, with the highest content in bovine colostrum. Lactoferrin in blood is mainly secreted by polymorphonuclear cells, and small amounts are also secreted by bone marrow, salivary glands, and the endometrium.
The concentration of lactoferrin in human milk is approximately 1.0-3.0 mg/mL, which is 10 times that in cow's milk (0.02-0.35 mg/mL in cow's milk), accounting for 20% of total protein in normal human milk. During lactation, the lactoferrin content changes with lactation time. For example, in human colostrum, lactoferrin can reach 6-14 mg/mL, dropping to 1 mg/mL in mature milk. On the first day after delivery, the lactoferrin content in cow colostrum can reach 1 mg/mL. The lactoferrin content in cow's milk also rises again at the end of lactation.
Bovine lactoferrin is a polypeptide chain with 703 amino acid residues, which folds into two基本上 symmetrical and highly homologous lobe-like structures (N-lobe and C-lobe). Studies suggest that this structure may have formed due to gene duplication during evolution. The N-lobe contains amino acids 1–332, and the C-lobe contains amino acids 344–703, connected by a hinge region, each about 40 kDa. The N-lobe and C-lobe can be further divided into N1, N2 regions and C1, C2 regions, respectively. The N-lobe carries a higher positive charge compared to the C-lobe. The N-lobe structure has been confirmed to be related to enhancing the antibacterial activity of lactoferrin, while the C-lobe structure can play a role in the treatment of stomach diseases, diabetes, and corneal injuries. Lactoferrin has two metal ion binding sites, each containing two tyrosines, one aspartic acid, and one histidine, which can reversibly bind one Fe3+ ion and one CO32- ion. Because the complex of lactoferrin with iron ions is red, it is also called "red protein".
Content source: Baidu Baike: https://baike.baidu.com/item/%E4%B9%B3%E9%93%81%E8%9B%8B%E7%99%BD/3407131?fr=aladdin