Crystallization and properties of staphylococcal leukocidin

Two components (F and S) of leukocidin were isolated and purified from broth culture of V8 strain of Staphylococcus aureus. There was loss of leukocidin activity during the separation, which was regained by mixing the components. Each component was apparently homogeneous by several criteria. The F and S components were crystallized (by salting out with saturated (NH4)2SO4 at pH 7.0) in the form of square plates and very fine needles, respectively, and the molecular weights of the components were approx. 32 000 and 31 000, respectively. The isoelectric points of the F and S components were pH 9.08 and 9.39, respectively. No detectable half-cystine and free sulfhydryl groups were found in either component. Amino-terminal amino acid analysis of both components showed a single alanine residue. The F and S components of leukocidin acted synergistically on granulocytes from rabbit peripheral blood and a minimum lethal dose of 0.5 ng of each component destroyed all granulocytes at a concentration of 10(6) cells/20 microliter.