Nonspecific adsorption of transferrin to K562 cell membrane

In the absence of albumin, incubation of K562 cells with radiolabeled transferrin revealed a binding component with high affinity and one with low affinity. The component with low affinity was eliminated in the presence of albumin, indicating it results from non-specific adsorption of ligand to cell membrane. The lack of specificity was further confirmed by demonstration that this component could be dissociated by pronase but not by acid. The high affinity component was responsible for most or all of the iron uptake by the cell. However, in certain cell densities of the culture, some iron could be taken up via other mechanisms. Therefore, the mechanism of low affinity binding could contribute to iron uptake by the cell in certain proliferative states.