Mechanism of control of erythrocyte shape: a possible relationship to band 3.

A mechanism of control of erythrocyte shape, differing significantly from those previously proposed, is hypothesized. It was inferred from previous observations on the states of association of Band 3, the anion exchange protein. Its salient points are as follows. (i) The membrane skeleton is a pliable protein meshwork structure used to generate different erythrocyte shapes. (ii) Band 3 is a dodecamer bound by one of its subunits to ankyrin which is itself bound to the mid region of filamentous spectrin. (iii) Spectrin, by virtue of its high flexibility, folds and unfolds and its folding links the two actin protofilaments bound at its ends to Band 3 through the intermediary of Band 4.1 and glycophorin A. (iv) The alternate influx and efflux of anions mediated by Band 3 respectively folds and unfolds spectrin. (v) The ratio of Band 3 molecules with outward-facing conformation to those with inward-facing conformation controls the extents of folding of the skeleton spectrin molecules. This ratio is governed by the Gibbs-Donnan equilibrium ratio of anions and protons and by the Band 3 anion affinities and exchange rates.