ABSTRACT
Diphtheria toxin and Pseudomonas exotoxin A are produced as single peptide chains. 1 Both proteins are organized into three physically and functionally distinct domains. Two of these domains are concerned with the binding of the toxins to receptors on cell surfaces and penetration of the cell membrane. The third domain enters the cytoplasm and functions catalytically to inhibit protein synthesis. It is this inhibition of protein synthesis that is responsible for the lethal effects of these toxins (see Perentesis et al., 1992a).
