The enzyme components of anthrax toxins cya (also known as EF, Edema Factor - Robertson et al. 1988) and lef (also known as LF, Lethal Factor - Bragg & Robertson 1989; Klimpel et al. 1994) bind to pagA(197-794):ANTXR1 (protective antigen, large fragment: Anthrax receptor 1) oligomers on the target cell surface. Binding of the two toxins to an oligomer is competitive and as many as four toxin molecules can bind to one oligomer (Elliott et al. 2000; Pimental et al. 2004).