Oligomeric states of spectrin in normal erythrocyte membranes: biochemical and electron microscopic studies.

We estimated the relative amounts of oligomeric species of spectrin in 0 degrees C red-cell-membrane extracts, including those released from spectrin-actin-polypeptide 4.1 complexes after mild urea treatment. Spectrin dimers, tetramers, and medium-size oligomers were the prominent species, accounting for 5%-10%, 45%-55%, and 25%-35% of spectrin, respectively. When examined by low-angle rotary-shadowing electron microscopy, these medium-size spectrin oligomers (e.g., hexamers, octamers, decamers , dodecamers , and quadecamers ) appeared as polyskelions formed by head-to-head association of three to seven dimers. They were stable species capable of binding to, and subsequent release from, inside-out vesicles without degradation to tetramers or dimers. The data suggest that spectrin tetramers and medium-size oligomers coexist in the normal erythrocyte membrane as the primary native spectrin species.