Адам ағзасындағы темір тасымалдаушысы – трансферрин

Mammalian protein found in Homo sapiens

Transferrins are glycoproteins found in vertebrates which bind and consequently mediate the transport of iron (Fe) through blood plasma. They are produced in the liver and contain binding sites for two Fe3+ ions. Human transferrin is encoded by the TF gene and produced as a 76 kDa glycoprotein. Transferrin glycoproteins bind iron tightly, but reversibly. Although iron bound to transferrin is less than 0.1% (4 mg) of total body iron, it forms the most vital iron pool with the highest rate of turnover (25 mg/24 h). Transferrin has a molecular weight of around 80 kDa and contains two specific high affinity Fe(III) binding sites. The affinity of transferrin for Fe(III) is extremely high (association constant is 1020 M−1 at pH 7.4) but decreases progressively with decreasing pH below neutrality. Transferrins are not limited to only binding to iron but also to different metal ions. These glycoproteins are located in various bodily fluids of vertebrates. Some invertebrates have proteins that act like transferrin found in the hemolymph. When not bound to iron, transferrin is known as "apotransferrin" (see also apoprotein).

Transferrins are glycoproteins that are often found in biological fluids of vertebrates. When a transferrin protein loaded with iron encounters a transferrin receptor on the surface of a cell, e. g., erythroid precursors in the bone marrow, it binds to it and is transported into the cell in a vesicle by receptor mediated endocytosis. The pH of the vesicle is reduced by hydrogen ion pumps ( ATPases) to about 5.5, causing transferrin to release its iron ions. The main role of transferrin is to deliver iron from absorption centers in the duodenum and white blood cell macrophages to all tissues. Transferrin plays a key role in areas where erythropoiesis and active cell division occur.

Transferrin is also associated with the innate immune system. It is found in the mucosa and binds iron, thus creating an environment low in free iron that impedes bacterial survival in a process called iron withholding. The level of transferrin decreases in inflammation.

An increased plasma transferrin level is often seen in patients with iron deficiency anemia, during pregnancy, and with the use of oral contraceptives, reflecting an increase in transferrin protein expression. When plasma transferrin levels rise, there is a reciprocal decrease in percent transferrin iron saturation, and a corresponding increase in total iron binding capacity in iron deficient states

A decreased plasma transferrin level can occur in iron overload diseases and protein malnutrition. An absence of transferrin results from a rare genetic disorder known as atransferrinemia, a condition characterized by anemia and hemosiderosis in the heart and liver that leads to heart failure and many other complications as well as to H63D syndrome. Studies reveal that a transferrin saturation (serum iron concentration ÷ total iron binding capacity) over 60 percent in men and over 50 percent in women identified the presence of an abnormality in iron metabolism (Hereditary hemochromatosis, heterozygotes and homozygotes) with approximately 95 percent accuracy. This finding helps in the early diagnosis of Hereditary hemochromatosis, especially while serum ferritin still remains low. The retained iron in Hereditary hemochromatosis is primarily deposited in parenchymal cells, with reticuloendothelial cell accumulation occurring very late in the disease. This is in contrast to transfusional iron overload in which iron deposition occurs first in the reticuloendothelial cells and then in parenchymal cells. This explains why ferritin levels remain relative low in Hereditary hemochromatosis, while transferrin saturation is high. Transferrin and its receptor have been shown to diminish tumour cells when the receptor is used to attract antibodies. Due to this functionality, it is theorized that nanoparticles acting as drug carriers bound to transferrin glycoproteins can penetrate the blood brain barrier allowing these substances to reach the diseased cells in the brain. Advances with transferrin conjugated nanoparticles can lead to non invasive drug distribution in the brain with potential therapeutic consequences of central nervous system (CNS) targeted diseases (e. g. Alzheimer's or Parkinson's disease).

Carbohydrate deficient transferrin increases in the blood with heavy ethanol consumption and can be monitored through laboratory testing. Transferrin is an acute phase protein and is seen to decrease in inflammation, cancers, and certain diseases (in contrast to other acute phase proteins, e. g., C reactive protein, which increase in case of acute inflammation).

Atransferrinemia is associated with a deficiency in transferrin. In nephrotic syndrome, urinary loss of transferrin, along with other serum proteins such as thyroxine binding globulin, gammaglobulin, and anti thrombin III, can manifest as iron resistant microcytic anemia.

An example reference range for transferrin is 204–360 mg/dL. Laboratory test results should always be interpreted using the reference range provided by the laboratory that performed the test. A high transferrin level may indicate an iron deficiency anemia. Levels of serum iron and total iron binding capacity (TIBC) are used in conjunction with transferrin to specify any abnormality. See interpretation of TIBC. Low transferrin likely indicates malnutrition.

Transferrin has been shown to interact with insulin like growth factor 2 and IGFBP3. Transcriptional regulation of transferrin is upregulated by retinoic acid.

Members of the family include blood serotransferrin (or siderophilin, usually simply called transferrin); lactotransferrin (lactoferrin); milk transferrin; egg white ovotransferrin (conalbumin); and membrane associated melanotransferrin.