Measurement of Bound and Free Endotoxin by the Limulus Assay (38240)

James H. Jorgensen, Rodney F. Smith

Research output: Contribution to journalArticlepeer-review

8 Scopus citations


The Limulus assay was used to measure activities of naturally occurring and chemically extracted endotoxins and endotoxin fractions. Large amounts of both bound and free endotoxin were detected from gram-negative bacterial cells grown in either enriched or minimal media, and from resting cells. Following purification by phenol extraction, free endotoxin evidenced a similar level of activity to that of bound endotoxin. Lipid A and polysaccharide prepared by hydrolysis of endotoxin demonstrated reduced Limulus activity. However, R-strains from three species of gram-negative bacilli produced large amounts of free endotoxin. These results indicate that free endotoxin is part of the LPS that is readily released in a liquid environment, and probably is composed of lipid A and core material. In addition, a relatively constant amount of endotoxin remains bound on the cell surface, allowing an approximate quantitation of viable bacilli in fluids using the Limulus assay.

Original languageEnglish (US)
Pages (from-to)1024-1031
Number of pages8
JournalProceedings of the Society for Experimental Biology and Medicine
Issue number4
StatePublished - Sep 1974

ASJC Scopus subject areas

  • Biochemistry, Genetics and Molecular Biology(all)


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