Bioendo rCR Endotoxin Test Kit (Recombinant Cascade Reagents Chromogenic Assay) uses gene recombinant technology to express Factor C pathway serine zymogen proteases of horseshoe crab amebocyte in eukaryotic cells. The cascade reagents include Factor C which can be activated by bacterial endotoxins, Factor B and proclotting enzyme. Endotoxins bind to and convert Factor C to its active form, which subsequently activates Factor B, which in turn activates the proclotting enzyme. The activated proclotting enzyme then cleaves chromogenic substrate, releasing a yellow-colored pNA. The released pNA can be measured photometrically at 405 nm. Based on which, the endotoxin concentration of test sample can be quantified. rCR endotoxin test kit does not use animal source materials, protects the horseshoe crabs.