(shē'gă )

Japanese bacteriologist, 1871–1957.

S. bacillus Shigella dysenteriae.

S. toxin An extremely poisonous compound secreted by enteric bacteria that causes hemorrhagic and necrotic colitis. The toxin was formerly called verotoxin because of its effect on Vero cells.

The toxin acts on the endothelial cells lining the blood vessels. The B subunits of the toxin bind to a component of the cell membrane known as Gb3 and enter the cell. When the protein is inside the cell, the A subunit interacts with the ribosomes to stop protein synthesis. Like the ricin toxin, the A subunit of Shiga toxin is an N-glycosidase that modifies the RNA component of the ribosome to stop protein synthesis, leading to the death of the cell. The breakdown of the endothelial cell lining leads to hemorrhage.