The role of mucosal iron binding proteins in adaptation of iron absorption during protein deficiency and rehabilitation

Abstract

1. A state of protein deficiency has been produced in rats by feeding a low protein diet, thereafter a period of rehabilitation with a normal protein but a low iron supply followed. 2. For characterization of the iron metabolism during both periods haemoglobin, total iron binding capacity, liver non-haemin iron, intestinal iron absorption and the uptake of 59Fe in the liver was determined. 3. Under these conditions the amount of 59Fe incorporated into the mucosal transferrin and the ferritin fractions has been measured. Both fractions were obtained from the supernatant of a mucosal homogenate after chromatography on sepharose 6B. 4. In anemia due to protein deficiency the typical increase of 59Fe incorporation into the fraction of mucosal transferrin--usually occuring in iron deficiency--could not be observed. This coincides with the absence of an increased iron absorption. Moreover a decrease of iron absorption is observed, which is associated with a decreased 59Fe ratio of transferrin/ferritin-fraction. 5. After normalization of the protein supply the ratio of 59Fe incorporated into the mucosal transferrin and ferritin fractions was changed remarkably in favor to transferrin together with a several fold increase of the intestinal iron absorption. 6. The conclusion is drawn that mucosal transferrin and ferritin enable the body not only to adapt the absorption to a higher but also to a lower requirement as it is the case in protein deficiency.

Binding of copper to mucosal transferrin and inhibition of intestinal iron absorption in rats

“…Whether this has a functional meaning for the epithelial iron transfer, remains an open question. In any case the 59Fe labelling of this fraction IV is under our conditions a regular observation in the snpernatant of normal and iron deficient animals [3,4]. In summary iron and copper have in common the affinity to the mucosal transferrin and metallothionein.…”

“…For the sake of clearness it is omitted in the other three diagrams. The typical UV-absorbance curves for groups of normal and iron deficient rats is given in Figure 2 of a former publication [4]. In the first diagram (left upper part of Fig.…”

“…Only iron is bound to the material of fraction V as represented by a peak which is remarkably increased in iron deficiency [4] and which coincides with a high peak of UV-absorbance. Obviously, this material of a molecular weight below 10,000 has no or at least a very low affinity to copper.…”

“…The approximate values for the dissociation constants of copper and iron ovotransferrin calculated are 10-17 and 10 -29 respectively [25]. This displacement of copper by iron is particularly clearly exemplified in iron deficiency, where the mucosal transferrin is the dominating iron binding protein in the supernatant [4]. The change of distribution within the supernatant occurs preferentially in favor of fraction IV but this is not the only binding material which takes over the copper displaced by iron.…”