Effects of Tannic Acid on Erythrocyte Enzymes

Abstract

MANY properties of the red cell have been studied with the aid of tannic acid since the original observations by Roberts¹. Treatment with this acid causes reduction in anion permeability², agglutination³, alterations in osmotic resistance⁴ and renders erythrocytes capable of adsorbing proteins from solution⁵. The latter characteristic serves as a basis for the widely used procedures of passive haemagglutination. We have shown that the exposure of human erythrocytes to tannic acid, in conditions commonly employed in passive haemagglutination techniques, results in irreversible inactivation of acetylcholinesterase (AChE)⁶. The effect on this membrane enzyme⁷ was dependent on concentration, pH, time and temperature. Although the mechanism by which tannic acid exerts its action on the red cell has not been elucidated, it has been suggested that in low concentrations this agent traverses the erythrocyte membrane⁴. To test this hypothesis we have investigated the effect of tannic acid on two intracellularly located enzymes, glucose-6-phosphate dehydrogenase (G6PD)⁸ and acid phosphatase⁷.