Interaction of Streptolysin-O with Natural and Artificial Membranes

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Abstract
Kinetic studies on the binding 125I-streptolysin-O exhibited immediate fixation of activated toxin to natural [sheep red blood cells] and artificial membranes. Once fixed to the membrane, no release of streptolysin-O or streptolysin-O-lipid-complexes was observed. Unlike activated toxin with free SH-groups, oxidized streptolysin-O became fixed to membranes with different binding kinetics. The binding of oxidized material was clearly dependent on temperature and time. When the toxin was oxidized, twice the amount of labeled material was bound as compared with the hemolytically active streptolysin-O. Oxidized streptolysin-O possesses a binding site within the molecule, though free SH-groups were essential for toxin fixation at the membrane. Oxidized (inactive) and reduced (active) streptolysin-O form stable complees with liposomes in aqueous solution, which could be separated by chromatography on Sepharose gels. The binding of 125I-toxin to membranes and liposomes was specific, since specific antisera [from humans] against streptolysin-O inhibited fixation of toxin completely. Hydrolysis of phospholipids and release of lysophosphatides by streptolysin-O esterase (EC 2.1.1.2) was not observed, thus providing no evidence for an enzymatic membrane damage.

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