The behavior of the botulinus toxins in the ultracentrifuge

Abstract

1. 1. Measurements of the sedimentation rate and diffusion constant of two specimens of type A botulinus toxin at pH 38–44 indicate a molecule of weight about 940,000 and axial ratio 17.5. 2. 2. The molecular weight of the type B toxin determined similarly at pH 3.0 was about 500,000 with an additional more slowly sedimenting component ( s 20 w = 10.7) representing about 30% of the material. 3. 3. Over the range pH 3.98-1.7, the type A toxin is monodisperse or paucidisperse with a main component whose sedimentation constant is not significantly pH-dependent. 4. 4. In the isoelectric region (pH ~ 5.5) the material becomes polydisperse with a maximum average sedimentation constant of about 28 for a 0.1% solution at or near the isoelectric point. 5. 5. At pH 7.5 about 14% of the material in a solution of type A toxin appeared as a second component of sedimentation constant 7. This component has been separated in the ultracentrifuge.