Substructure of human erythrocyte spectrin.

The human erythrocyte structural protein spectrin and its subunits I, II were isolated in the presence of Na-dodecyl-sulfate by gel filtration and preparative gel electrophoresis. After removal of the detergent, spectrin alpha-helical content is comparable to spectrin isolated without detergent. Subunits I and II formed single bands in isoelectric focusing (pI = 5.6) and in Ornstein-Davis disc gel electrophoresis systems, indicating the individual subunits are homogenous in nature. The molecular weights of the subunits I and II, determined by Ferguson plot, are 237,500 and 238,600, respectively, which is in good agreement with values obtained by the standard SDS gel relative mobility method. Limited tryptic digestion of spectrin and two-dimensional peptide maps of the individual subunits cleaved by S-cyanylation reaction showed dissimilar patterns, suggesting differences in primary structure between the two subunits.