2D gels of tryptic peptides from spectrin dimers and α dimerization site recombinant peptides. Isofocusing was in the horizontal direction (basic side on the left) followed by separation on a 12% SDS gel that was stained with Coomassie Brilliant Blue. (A) Two hundred micrograms of spectrin digested with trypsin from a normal donor; (B) 200 μg of spectrin digested with trypsin from a donor homozygous for the α^LELY mutation; (C through E) 20 μg of each recombinant spectrin peptide digested with trypsin. (C) α18-21; (D) α18-21¹⁸⁵⁷; (E) α18-21^1857-Δ46. Arrows indicate the position of the normal αV 41-kD tryptic domain in all panels. The arrowheads indicate the major αIV domain peptides in (A) and (B).