Inability to detect transferrin receptors on P. falciparum parasitized red cells

The mechanism by which P. falciparum takes up iron from transferrin has been explored. Binding of ¹²⁵I labelled transferrin to parasitized red cells at 37°C is two-fold greater than to control cells; at 0°C there is no significant difference. The binding is non-specific as judged from the following: it is not saturable; it is not limited to transferrin as lactoferrin (which has iron binding domains) and bovine serum albumin (which does not) also bind in excess to parasitized red cells. A transferrin receptor complex could not be demonstrated when parasitized red cells, to which ¹²⁵I transferrin was bound, were solubilized in Triton X100. Previous observation showed that uptake of transferrin iron by parasitized red cells is not accompanied by equimolar uptake of transferrin protein. We therefore suggest that non-specifically bound transferrin is endocytosed, that the protein is degraded and the iron selectively retained.