Abstract

α-Hemolysin (HlyA), an extracellular protein toxin produced by some pathogenic strains of Escherichia coli , is known to disrupt eukaryotic cell membranes. In an attempt to correlate the structure of this toxin with its function, we studied the role of the histidine residues on the toxin activity by their chemical modification with the reagent diethyl pyrocarbonate (DEPC). The results of this study suggest the presence of an essential histidine residue at the Ca²⁺-binding motif and it.s role in the lytic action of E.coli HlyA.