Binding of positively charged particles to glutaraldehyde-fixed human erythrocytes

Abstract

A combined electrokinetic and electronmicroscopic study was made of the negatively charged sites at the surfaces of glutaraldehyde-fixed, human erythrocytes with and without prior incubation with neuraminidase. The spatial distribution and densities of positively charged, colloidal iron hydroxide markers, adsorbed to the negatively charged surface anionic groups, was statistically analysed from electron micrographs. It was observed that the loss of net surface negativity following neuraminidase-treatment, was accompanied by a highly significant, but disproportionate reduction in particle binding. In addition, following enzyme treatment the adsorbed particles showed a departure from the uniform distribution observed in the controls. The findings are speculatively interpreted to indicate that the neuraminidase-susceptible sialic acids at the surface of human erythrocytes are arranged in clusters having a higher than average charge density. The clusters themselves are distributed uniformly over the cell surface. It is suggested that this latter arrangement would partially account for the non-adhesiveness of human erythrocytes under many conditions.