Characteristics of lipid A-protein complex from endotoxin of Shigella dysenteriae type 1 (S and R strains).

Mild acetic acid hydrolysis of endotoxin (lipopolysaccharide-protein complex) of Shigella dysenteriae type 1 (S and R forms) yielded a lipid A-protein complex that consisted of amino acids, fatty acids, and sugar and, in terms of chemical composition, displayed no marked differences between the S and R forms. Its protein portion (53 to 56%) consisted of at least 16 amino acids. In the fatty acid portion (14 to 18%), myristic, 3-hydroxymyristic, palmitic, and stearic acids accounted for 50%. The sugar portion (10 to 12%) consisted solely of glucosamine. The remainder was unidentified substances, most of which contained phosphorus. Lipid A-protein complexes derived from both S and R forms were not toxic for mice in doses up to 1,000 microgram/mouse, but their Linulus test activity had increased considerably as compared with the starting lipopolysaccharide-protein complex material: from 10(-6) to 10(-10--10(-12) mg/ml. The lipid A-protein complexes were readily soluble in a water solution of triethylamine, in dimethyl sulfoxide, and in pyridine.