Streptolysin O, a group A streptococcal toxin, is a well-characterized oxygen-labile prototype of a cholesterol-binding bacterial exotoxin. Streptolysin O causes both lysis of cells and cardiotoxicity. Streptolysin O is widely used for the controlled permeabilization of cell membranes. Streptolysin O exists in two forms, a reduced active state and an oxidized reversibly inactive state[1][2][3][4].