Transferrin, plasma transport

Transferrin Iron transport in plasma and into cells hpx mice (Huggenvik et al, 1989 Bernstein, 1987 Craven et al, 1987 Goya et al, 1972) Hypotransferinemia (Goya et al., 1972) microcytic anaemia increased iron absorption parenchymal iron overload... 

Schade reviewed (114) the earlier studies on the role of serum transferrin in iron transport. Various early investigators had observed that the blood serum transferrin rapidly bound iron administered either through the gastrointestinal tract or by intravenous injection. There was a rapid turnover of iron in the blood serum and the degree of saturation of the transferrin was related to the amount of iron administered. In no instances, however, was the blood serum transferrin ever saturated with iron. Jandl et al. (71) have shown that both ovotransferrin and serum transferrin can transport plasma iron into red cells and that the transport is dependent on the concentration of transferrin. Iron taken up by the blood cells could not be eluted by subsequent incubation with iron-free transferrin solutions. More recently Morgan and Laurel (99) reported that iron uptake in reticulocytes is independent of the transferrin concentration. The iron complex of serum transferrin has a higher affinity for immature red cells than does the iron-free protein (72). Both bind specifically to immature red cells and the attachment permits the cells to remove the iron. Once the iron is removed, however, the iron-free transferrin can be replaced by an iron-transferrin complex. 

Ascorbate is also active in the reduction of Fe + in the plasma transport protein, transferrin, to Fe + for storage in ferritin in the Uver or for heme synthesis. It is not clear to what extent this represents specific actions of ascorbate, because other reducing reagents, including glutathione, also enhance heme synthesis, and the NADH-dependent flavoprotein ferriductase is the major factor controlling the transfer of iron between transferrin and ferritin. 

Transferrin (originally named siderophilin) is the principal plasma transport protein for iron (Fe " ) see Chapter 31. 

Transferrin Hepatocyte 8 Binds Fe in plasma transports Fe to bone Fe deficiency, pregnancy, hypoxia, chronic blood loss, estrogens Chronic infection, cirrhosis, burns, enteropathies, nephrotic syndrome, cortisone, testosterone... 

Transferrin (Tf) is a plasma protein that plays a centtal role in transporting iron around the body to sites where... 

Dosing for iron should be divided equally into two to three doses daily. An empty stomach (1 hour before or 2 hours after a meal) is preferred for maximal absorption. After absorption, iron binds to transferrin in the plasma and is transported to the muscles (for myoglobin), liver (for storage), or bone marrow (for red cell production). Iron is not actively excreted from the body but is lost through other measures already described.7 Some studies suggest that iron absorption may be... 

Figure 9.7 Iron transport by hepatocytes. Known proteins involved in iron transport across the plasma membrane of hapatocytes are represented. LMW = low molecular weight Trf = transferrin Trf-R = transferrin receptor HFE = hamochromatosis gene product 132m = 62-microglobulin 02-= superoxide OH- = hydroxyl radical FR = ferritin receptor SFT = stimulator of iron transport.

The determination of the structure of the iron transporter, ferric-binding, protein (hFBP)t from Haemophilus influenzae (Bruns et ah, 1997) at 0.16 nm resolution shows that it is a member of the transferrin superfamily, which includes both the transferrins and a number of periplasmic binding proteins (PBP). The PBPs transport a wide variety of nutrients, including sugars, amino acids and ions, across the periplasm from the outer to the inner (plasma) membrane in bacteria (see Chapter 3). Iron binding by transferrins (see below) requires concomitant binding of a carbonate anion, which is located at the N-terminus of a helix. This corresponds to the site at which the anions are specifically bound in the bacterial periplasmic sulfate- and... 

This receptor-mediated endocytotic pathway has been especially well studied in the uptake of iron from blood plasma. Iron, because of its very low-solubility product (< 1(T17 at pH 7.4), is transported in plasma bound to the iron-binding protein transferrin. Two Fe3+ ions bind to each transferrin molecule. Entry into... 

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