Pulse-chase analysis of metabolically labeled late erythroblasts. Late erythroblasts were labeled with [³⁵S]methionine for 60 minutes and then chased with unlabeled methionine for 16 hours. Plasma membranes isolated from unchased and chased cells were extracted with C₁₂E₈. (A) The C₁₂E₈extracts were subjected to size exclusion HPLC. (B) C₁₂E₈-insoluble pellets (P) and -soluble supernatants (S) were immunoprecipitated with anti–band 3 antibodies. The immunoprecipitates were analyzed by SDS-PAGE and the gels were processed for fluorography. (C) The autoradiograms shown in B were scanned and the area under each peak integrated (the autoradiograms for the 2-hour chase period are not shown). Band 3 dimers synthesized before the chase were stable and did not associate to form tetramers during the 16-hour chase period.