Interaction of Bacterial Endotoxins with Chitosan. Effect of Endotoxin Structure, Chitosan Molecular Mass, and Ionic Strength of the Solution on the Formation of the Complex

V. N. Davydova^*, I. M. Yermak, V. I. Gorbach, I. N. Krasikova, and T. F. Solov'eva

Pacific Institute of Bioorganic Chemistry, Far East Division of the Russian Academy of Sciences, pr. 100-letiya Vladivostoka 159, Vladivostok, 690022 Russia; fax: 7 (4232) 31-4050; E-mail: piboc@stl.ru

^* To whom correspondence should be addressed.

Received January 19, 2000; Revision received May 20, 2000

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The interaction of endotoxins of different structure (lipopolysaccharides (LPS) and lipopolysaccharide-protein complexes (LPPC)) with chitosan has been studied. It was shown that the mechanism of interaction is rather complicated and depends on the macromolecular organization of endotoxin as well as on the degree of polymerization of the chitosan. Chitosan with molecular mass of 20 kD reveals higher affinity to LPS than chitosan with molecular mass of 140 kD. Endotoxins with long O-specific chains can bind completely with chitosan with the formation of LPS-chitosan and LPPC-chitosan complexes with weight ratios between the original components of 1 : 1 and 1 : 5. When endotoxins with higher degree of hydrophobicity and short O-specific chains were mixed with chitosan, a part of the LPS remained unbound. The stability of the complexes formed depends on ionic strength. It was shown that, in addition to electrostatic forces, other types of forces take part in the formation of the complexes. A decrease in acute toxicity of various LPSs is observed on their binding with chitosans.

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KEY WORDS: endotoxin, lipopolysaccharide, lipopolysaccharide-protein complex, chitosan, interaction, centrifugation

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