Physical states of staphylococcal alpha-toxin.

At least three different forms of staphylococcal alpha-toxin have been shown to exist: soluble active alpha-toxin (alpha 3S), soluble inactive alpha-toxin (alpha(12s)), and insoluble inactive aggregate. Aggregation to the insoluble, biologically inactive form could be induced by brief heating to 60 C. The aggregate was dissociated by treatment with 8 m urea with reappearance of biological activity. Subsequent removal of urea by dialysis resulted in some spontaneous reaggregation to the insoluble state. The supernatant fluid obtained after dialysis contained soluble active alpha-toxin of high specific activity, possessing physical, toxic, and immunological properties closely resembling those of native toxin. The soluble biologically inert component (alpha(12s)) was identified as a third physical state. Negatively stained preparations of this material, when examined in the electron microscope, showed rings of approximately 100 A outside diameter containing 6 +/- 1 subunits.