The influence of some cations on bacterial endotoxins: copper

In the course of its isolation and purification, bacterial endotoxin may be contaminated by some inorganic cations. The present study was concerned with Cu-2+ contamination of the lipopolysaccharide-protein complex (LPS) extracted from Shigella dysenteriae 1 S and R strains. The Cu-2+ contamination level of LPS prepared by Raynaud's method and partly purified through Sephadex G200 and Sepharose 4B was in the range of 1-5 mug Cu-2+/mg LPS. Crude Raynauds extract, similarly as LPS prepared by Westphal's method without subsequent purification, contained 0.02-0,1 mug Cu-2+/mg LPS. The linkage of Cu-2+ to LPS was relatively weak; the Cu-2+ content could be substantially reduced, viz. to 0.05-0.1 mug/mg, by dialysis against solutions of suitable complex-forming agents (EDTA, DL-alpha alanine). Neither a grossly augmented (up to 60 mug/mg) nor a lowered Cu-2+ concentration (0.02 mug/mg) had any appreciable influence on the toxicity or other biological properties of LPS. Attention is drawn to this ability of LPS to bind and again readily release a relatively large amount of Cu-2+ and the possibility that this ability is utilized by the bacterial cell in Cu-2+ transport through the cell membrane.