Ultracentrifugal Analysis of Staphylococcal Alpha Toxin

Abstract

Ultracentrifugal examination of staphylococcal alpha toxin at different stages of purification showed the presence of a major component having a sedimentation coefficient of 2.8 S , present to the extent of more than 90% of the sample, and identifiable with active toxin. Several minor components having S 20,w values of 11.5 S , 8.5 S , and 2.0 S were detected. The 11.5 S component presumably is identical with a toxin aggregate studied earlier and designated 12 S ; the 8.5 S component appears to be delta toxin. A sedimentation equilibrium study of more highly purified material gave 32,700 as the best estimate of molecular weight of alpha toxin. Lowering the p H of the partially purified alpha toxin from 10.2 to 5.3 resulted in a small increase in S 20,w of the 11.5 S component and in the disappearance of the 8.5 S component, whereas the S 20,w , molecular weight, and hemolytic activity of the toxin remained constant. Exposure of toxin to p H 3.5 irreversibly reduced the S 20,w to 2.0 S , the molecular weight to about 16,000, and caused irreversible inactivation. Raising the p H of acid-inactivated toxin and adding sodium dodecyl sulfate to 1% increased the S 20,w to near its normal value (2.7 S ) but did not restore activity.