Isolation and characterization of the heat stable enterotoxin from a pathogenic bovine strain of Escherichia coli.

A heat-stable enterotoxin secreted by a pathogenic strain of Escherichia coli of calf origin was purified to homogeneity by a procedure involving acetone fractionation, DEAE cellulose chromatography, Biogel P2 chromatography and size exclusion high pressure liquid chromatography. The purity of the product was ascertained by amino-acid analyses and amino acid sequence using manual degradation with 4-N, N dimethylaminoazobenzene-4' isothiocyanate (DABITC) and an automatic gas phase sequenator. The following amino acid sequence is proposed: Asn-Thr-Phe-Tyr-Cys-Cys-Glu-Leu-Cys-Cys-Asn-Pro-Ala-Cys-Ala-Gly-Cys-Tyr. It is identical to a similar active peptide isolated from strains of porcine origin. Antibodies to ST were successfully produced in rabbits using a conjugate with bovine serum albumin. The ultraviolet absorption and circular dichroism spectra of the active product were recorded and discussed.