Endotoxin
Endotoxin — A lipopolysaccharide from gram-negative bacterial cell walls that can contaminate peptide preparations, detected by the Limulus amebocyte lysate (LAL) assay.
What Is Endotoxin?
Endotoxin (lipopolysaccharide, LPS) is a component of the outer membrane of Gram-negative bacteria that triggers a potent inflammatory response in mammalian cells. Even trace amounts (< 1 ng/mL) can activate macrophages and dendritic cells through TLR4, producing cytokine storms that confound experimental results in in vitro and in vivo peptide studies.
Testing Methods
- LAL (Limulus Amebocyte Lysate): The gold standard assay using horseshoe crab blood extract that clots in the presence of endotoxin. Sensitivity: 0.01-0.1 EU/mL
- rFC (Recombinant Factor C): A synthetic alternative to LAL that avoids horseshoe crab harvesting
- Kinetic turbidimetric: Automated LAL variant measuring clot formation rate for quantitative results
Acceptable Limits
Research-grade peptides for cell culture should contain < 1 EU/mg. In vivo grade material requires < 0.25 EU/mg or lower depending on dose and route. The Certificate of Analysis should report LAL test results for any peptide intended for biological assays. Endotoxin contamination is the most common reason for unexplained inflammatory responses in peptide research.
Frequently Asked Questions
What is Endotoxin?
A lipopolysaccharide from gram-negative bacterial cell walls that can contaminate peptide preparations, detected by the Limulus amebocyte lysate (LAL) assay.
Why is Endotoxin important in peptide research?
Endotoxin is a fundamental concept in quality as it relates to peptide science. It directly influences experimental design, compound characterization, and the reliability of research outcomes across biochemistry and molecular biology disciplines.