The surface charge of human glutaraldehyde-fixed erythrocytes

We measured the number of charged residues at the surface of fresh human erythrocytes after fixation with glutaraldehyde by polyelectrolyte titration using polycations of different chemical composition and various molecular weights. Independent of the reagents used, the number was (8.5 +/- 1.5) X 10(8) negatively charged residues per cell. The surface charge density of 6.3 e/nm2 is considerably higher than that calculated from the electrophoretic mobility for which the surface charge density is calculated to be 0.09 e/nm2.