The uptake of iron by reticulocytes. The influence of purification of the ghosts on iron-containing components in the ghost suspension.

1. Rat reticulocytes previously incubated with ((59)Fe, (125)I)-labelled transferrin were hemolysed to yield labelled ghosts. 2. The solubilized ghosts can be fractionated, by gel filtration on Sepharose 2B and 6B, into several (59)Fe- and (125)I-containing compounds, classified as A, B(1) and B(2). 3. These fractions were prepared from ghosts which were obtained at different centrifugation rates and further purified by sucrose density gradient centrifugation in order to obtain membrane compounds purified from mitochondrial and lysosomal impurities. The influence of these purification steps on the appearance and the (59)Fe/(125)I activity of the three components was investigated. 4. The first Sepharose 2B fraction with high molecular mass, greater than 10(6) daltons, is an intracellular product of mitochondrial and lysosomal origin which precipitates with the membrane fractions during the preparation of the ghost. The first Sepharose 6B fraction, B(1), with M(r) approximately 10(6) seems to be a real membrane component. The second Sepharose 6B fraction, B(2), with M(r) approximately 230 000 represents a real membrane receptor transferrin.