Isolation and function of a Clostridium perfringens enterotoxin fragment.

A fragment was obtained by treating Clostridium perfringens enterotoxin with 2-nitro-5-thiocyanobenzoic acid, a reagent which specifically cleaves the amino-terminal peptide bond of cysteine residues. The fragment (molecular weight, 15,000) was purified by high-performance liquid chromatography. The fragment had no cytotoxic effect on Vero cells but competitively inhibited enterotoxin-induced 51Cr release. Binding of 125I-labeled fragment to Vero cells was comparable to that of enterotoxin. Moreover, 125I-labeled fragment did not bind to FL cells, which lack receptor for enterotoxin. We conclude that the fragment contains the binding domain of enterotoxin. The amino acid composition of the fragment suggests that it is located on the carboxyl-terminal part of enterotoxin.