Sialic Acid Content of the Erythrocyte and of an Ascites

92.6 (19). Sialic acids have been found on the eryth rocyte membranes of a number of vertebrate species (5, 7, 192). Viral or bacterial neuramini dases, enzymes which cleave the a-ketosidic link age between a terminal sialic acid group and a sugar or sugar derivative (9), can liberate free sialic acid from such red cell membranes (5, 7). The surface of the mammalian erythrocyte is neg atively charged with a reported isoelectric point of about pH 92.0 (1, 8). Following enzymatic re moval of sialic acid from the human erythrocyte, the isoelectric point of the red cell is greatly in creased, indicating that these groups are primarily responsible for the negative charge on the erythro cyte membrane (5, 7). The mouse Ehrlich ascites tumor (EAT) cell also has a negatively charged surface with a meas