AJP - Gastrointestinal and Liver Physiology, Vol 257, Issue 6 930-G934, Copyright © 1989 by American Physiological Society

ARTICLES

Fe-saturation and proteolysis of human lactoferrin: effect on brush-border receptor-mediated uptake of Fe and Mn

L. A. Davidson and B. Lonnerdal
Department of Nutrition, University of California, Davis 95616.

We have previously characterized a brush-border membrane receptor that facilitates iron uptake from human lactoferrin. The receptor is specific for human and monkey lactoferrin and does not recognize human transferrin or bovine lactoferrin. In this study, iron uptake from lactoferrin fragments was studied, as well as from lactoferrin partially saturated with iron. Brush-border membrane vesicles (BBMV) prepared from infant rhesus monkey small intestine efficiently accumulated iron from lactoferrin half-molecules, although competition experiments showed that intact lactoferrin has a higher affinity toward the receptor. Lactoferrin partially saturated with iron also effectively delivered iron to the receptor, whereas the affinity was lower than for lactoferrin saturated with iron. Lactoferrin also carries a large proportion of human milk manganese, and receptor-mediated uptake of lactoferrin-bound manganese into BBMV was demonstrated, although this complex had lower affinity than that found for iron-lactoferrin. Thus, although the receptor has a preference for intact iron-saturated lactoferrin, partially digested lactoferrin and partially iron-saturated lactoferrin can also deliver iron to the receptor. Therefore, these molecular species, which are likely to occur in the gastrointestinal tract of the infant, may contribute to the high degree of iron absorption from human milk lactoferrin.

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