Approximate dimensions of membrane lesions produced by streptolysin S and streptolysin O.

Membrane lesions produced by the streptococcal membranolysins streptolysin S and streptolysin O were investigated. Escape of labeled marker molecules of various sizes from resealed sheep erythrocyte ghosts treated with the toxins for 30 min allowed estimation of the sizes of the primary channels formed. Streptolysin S formed lesions ranging in size up to 45 A in diameter, and even high toxin concentrations did not result in larger channels. The lesions produced by streptolysin O exceeded 128 A in diameter. Kinetics experiments demonstrated that the primary streptolysin O lesions were formed rapidly (1-2 min), but release of marker molecules from streptolysin S-treated vesicles began only after a 5-15-min lag period. Label release from large unilamellar liposomes treated with streptolysin S suggested that membrane fluidity does not affect the size of the streptolysin S lesions.