Chemical synthesis of an octadecapeptide with the biological and immunological properties of human heat-stable Escherichia coli enterotoxin

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Abstract
An 18-amino-acid peptide having the linear amino acid sequence of human heat-stable enterotoxin (ST) was synthesized by solid phase peptide synthesis. The purified peptide could be obtained in yields approaching 25% after purification by size, charge and high-performance ligand chromatography. This material was pure and identical to native ST by analytical high-performance ligand chromatography, amino acid analysis, paper electrophoresis and TLC. The formation of the disulfide bonds was critical for biological and immunological activity and were tentatively determined to be between cysteines 5 and 14, 6 and 10 and 9 and 17. This synthetic peptide had full immunological and biological activity when compared to native ST by enzyme-linked immunosorbent assay and the suckling mouse assay, respectively.