Escherichia coli hemolysin permeabilizes small unilamellar vesicles loaded with calcein by a single-hit mechanism.

Escherichia coli hemolysin produces small unilamellar lipid vesicles permeable to the fluorescent dye calcein by forming pores through their membrane. The process of permeabilization proceeds as a pseudo first-order reaction, indicating that the toxin is active as a monomer; consistently no evidence for cooperativity has been found in a dose-response titration. The rate of interaction increases on lowering the pH of the solution and by introducing negatively charged lipids into the vesicles. The overall pore formation mechanism resembles that of other toxins of bacterial origin such as colicins, diphtheria, tetanus and botulinum toxin.