The Contribution of Sialic Acid to the Surface Charge of Fragments of Plasma Membrane and Endoplasmic Reticulum

In previous publications ( 1 ~ ) we have described the isolation from the microsomal fraction of Ehrlich ascites carcinoma (EAC) of two major membrane types, namely: (a) ER-type particles, arising primarily from the "smooth" endoplasmic reticulum, and (b) PM-type particles originating principally from the plasma membrane. We have also presented some details of the light-scattering properties of these membrane types, in particular the distinctive absorbance changes which accompany alterations of the ionogenic properties of the particles' surfaces (5). The present report is a continuation of these studies and deals with the contribution of neuraminic acid to the negative charge of PMand ER-type membranes.