Early events in guinea pig reticulocyte iron uptake.

Hemolysates, prepared from guinea pig reticulocytes incubated with 59Fe-labelled serum, can be resolved into five peaks utilizing molecular sieve chromatography: ferritin, transferrin, hemoglobin, an Mx 17 000 fraction, and a low molecular weight fraction. The hemoglobin peak also contains a nonhemoglobin component (III-X), demonstrated by heme extraction and by isoelectric focusing. Transferrin, the III-X component and the low molecular weight fraction are the first to accumulate radioactive iron during the reticulocyte incubation. The 59Fe in each of these also chases. Therefore, a role for these components as precursors to iron incorporation into heme is suggested.