On the mechanism of ATP induced shape changes in human erythrocyte membranes. I. The role of the spectrin complex

Human erythrocyte ghosts have been shown, by scanning electron microscopy, to undergo ATP-dependent shape changes. Under appropriate conditions the ghosts prepared from normal disk-shaped intact cells adopt a highly crenated shape, which in the presence of Mg-ATP at 37°C is slowly converted to the disk shape and eventually to the cup shape. These changes are not observed with other nucleotides or with 5'-adenylylimidodiphosphate. Anti-spectrin antibodies, incorporated along with the Mg-ATP into the ghosts in amounts less than equivalent to the spectrin, markedly accelerate the shape changes observed with the Mg-ATP alone. The Fab fragments of these antibodies, however, have no effect. The conclusion is that the structural effect produced by the ATP is promoted by the cross-linking of spectrin by its antibodies, and may therefore itself be some kind of polymerization or network formation involving the spectrin complex on the cytoplasmic face of the membrane. The factors that contribute to the shape of the ghost and of the intact erythrocyte are discussed in the light of these findings.