Biological and immunological characteristics of 125I-4Tyr and -18Tyr Escherichia coli heat-stable enterotoxin species purified by high-performance liquid chromatography.

A rapid procedure for the separation of Escherichia coli heat-stable enterotoxin iodination products is described. A two-step procedure using reverse-phase chromatography results in the separation of native, noniodinated heat-stable enterotoxins from several distinctly iodinated species which differ in their ability to bind to brush border receptors. Sequence analysis of the radioligands demonstrated mutually exclusive labeling at the 4Tyr and 18Tyr residues. These tracers have been immunologically and biologically characterized and have been shown to be antigenically similar but to differ in their toxicity for suckling mice. The radioligands separated by this procedure demonstrate stable behavior for a period of months.