Endotoxin in Recombinant Proteins: Why It Decides Your Cell-Based Assay

Endotoxin is invisible in a purity figure and decisive in a live-cell experiment. Here is what it is, where it comes from and when to specify it.

What endotoxin is and where it comes from

Endotoxin is lipopolysaccharide carried over from the host-cell envelope, which is why it is associated mainly with E. coli expression. It is not part of the protein sequence, so it cannot be designed out — it has to be removed by process and confirmed by testing.

Why it matters for some experiments and not others

In an ELISA or a Western blot, trace endotoxin is usually irrelevant. The moment living cells are involved — stimulation experiments, primary cells, signalling work — endotoxin is itself a potent stimulus and will mask the effect you actually set out to measure.

How it is specified and measured

The common grade is < 1.0 EU/µg; cell-based work usually calls for < 0.1 EU/µg, determined by the LAL method. State the endotoxin requirement in your enquiry rather than discovering it after the experiment fails — it is a specification, not an upsell.

Ask a technical question