Specific removal of endotoxin from protein solutions by immobilized histidine

Abstract

A method for reducing endotoxin contamination in various solutions by immobilized histidine is described. Immobilized histidine is a porous adsorbent suitable for the adsorption of endotoxin with a high affinity over a wide range of pH and temperature and at low ionic strength (gamma/2 less than or equal to 0.1). When a purified endotoxin originating from Escherichia coli UKT‐B was studied, the apparent dissociation constant between endotoxin and the adsorbent was 7.3 × 10(‐13) M. The adsorbent was able to remove various kinds of endotoxin originating from gram‐negative bacteria; the concentration of endotoxin was reduced from 1000 to less than 0.01 ng/ml in water. It is shown that the adsorbent specifically adsorbs endotoxin provided that the adsorption conditions are properly selected. Some examples of the specific removal of endotoxin from high‐molecular‐weight physiologically active substances such as tumor necrosis factor and lysozyme are shown.