Size-exclusion HPLC of C₁₂E₈extracts from (A) early erythroblast membranes, (B) late erythroblast membranes, and (C) late erythroblast membranes after spectrin extraction. Plasma membranes isolated from [³⁵S]methionine-labeled early and late erythroblasts were dissolved in 0.5% C₁₂E₈ in hypotonic buffer at 4°C. Samples were centrifuged at 150,000g for 30 minutes and the supernatants were analyzed by size-exclusion HPLC using a TSK-4000 SW_XL column. At the bottom of the HPLC profile are shown the elution positions for the standard proteins: T, thyroglobulin; F, ferritin; and A, aldolase. The void volume (V₀) was determined from the elution position of blue dextran 2000 (average molecular weight 2 × 10⁶ daltons). The tetramer (B3T) and dimer (B3D) peaks were examined by SDS-PAGE followed by autoradiography. Newly synthesized band 3 exists as tetramer in early erythroblasts and as dimer in late erythroblasts.