Improved method for purification of human Escherichia coli heat-stable enterotoxin by hydrophobic interaction, molecular-sieve and high performance ion exchange chromatography

A heat-stable enterotoxin produced by human enterotoxigenic Escherichia coli has been purified to homogeneity by hydrophobic interaction, molecular-sieve and high performance liquid chromatography with a recovery of 48%. The toxin is composed of 10 different amino acids with a total of 18 amino acid residues, one-third of which are half-cystine. Purified enterotoxin contains no carbohydrate and is biologically active in the suckling mouse test in 2.1-ng quantities. The molecule was heat-stable (80 degrees C, 20 min.) at pH 7 and pH 2 but lost biological activity at pH 12. Biological activity was lost when treated with the reducing agent dithiothreitol, suggesting that the presence of disulfide bridges is required for biological activity.