Iron binding proteins and influx of iron across the duodenal brush border. Evidence for specific lactotransferrin receptors in the human intestine.

The ability of a range of homologous transferrin-like proteins to donate iron to pieces of human duodenal mucosa, was examined with an in vitro incubation technique. In contrast to serum transferrin and ovotransferrin, only lactotransferrin was able to yield its iron to intestinal tissue, but in an autologous system this protein was unable to donate iron to human reticulocyte preparations. Studies with 125I-labelled lactotransferrin and lactotransferrin dual-labelled with 59Fe and 125I, indicated that the intact protein is excluded from entry into the enterocytes. The experiments suggest that iron may be transported across the brush border after delivery to specific protein binding sites at the cell surface.