SOME NEGATIVE CONTRAST STAINING FEATURES OF A PROTEIN FROM ERYTHROCITE GHOSTS

Negative contrast staining has been used to study a protein from erythrocyte ghosts. This protein has a quaternary conformation resembling a hollow cylinder built from a stack of four rings of protein subunits. The outer diameter of the hollow cylinder (tetramer) is estimated to be approximately 125 Å and the height approximately 170 Å. The hollow cylinder is thought to dissociate into single ring or torus structures, which show a tenfold rotational symmetry. The outer diameter of these tori is estimated to be approximately 130 Å and the thickness approximately 35 Å. The different electron images which the tetramer and single torus proteins produce in the electron microscope are presented. Negative contrast staining was carried out using both sodium phosphotungstate and uranyl acetate. A theoretical interpretation of the electron images produced by the side-on orientation of these molecules is put forward. The results are discussed, and compared with those from other protein molecules which show cylindrical shapes in the electron microscope. A general postulate is made that the hollow cylindrical protein assembly, composed of rings of subunits, is a thermodynamically stable quaternary conformation for the subunits of some proteins. © 1969.