Department of Microbiology, MFH-bygget, N-5016 Haukeland sykehus, Bergen, Norway.


A group of proteins was readily extracted at neutrality from trichloroacetic acid precipitates of staphylococcal culture filtrate supernatants, while α-toxin was dissolved and activated by treating the precipitate with 8 M urea, with acidic buffers or by heating to 90–100° C at neutrality. Heat activation of the precipitate produced a relatively pure α-toxin with a molecular weight of 39,000. α-Toxin was eluted together with three other proteins on hydroxyl apatite chromatography, and evidence was obtained for an association between the four proteins. On isoelectric focusing a haemolytic fraction was obtained at pH 6.2, probably due to acid activation of the precipitate formed at the cathodic end of the column. The α-haemolytic fractions with pI's of 7.4 and 8.6 were shown to consist of α-toxin only when analyzed by acrylamide electrophoresis in the presence of sodium dodecyl sulphate. The haemolytic component with a pI of 9.2 contained two additional components of molecular weights of 27,500 and 18,000. Chromatography of this material on Sephadex G-200 showed that α-toxin and the two proteins appeared as a high molecular complex.