Electron microscopy of the toxin and hemagglutinin of type A Clostridium botulinum.

Electron micrographs of the toxin and the hemagglutinin of type A Clostridium botulinum showed the toxin to be either round or disclike particles of 4 to 4.5 nm. These particles could also be seen as arranged in long strands or tubules of 9 nm in width. The hemagglutinin appeared as a crystalloid monolayer of stacked particles of 9 nm forming regularly arranged structures of 20 nm. Seen in cross section, these structures appeared as tubules with a lumen of 9 nm. The regularity of the angle of 83 degrees to the long axis of the structure in which the individual particles were arranged suggested that the hemagglutinins formed a helix with sufficient space within its coil to admit the strands of the toxins. A model of the possible arrangement of the toxin and the hemagglutinin in the native state is proposed.