E. coli ST vs LT

The ST enterotoxin is actually a family of toxins which are peptides of molecular weight about 2,000 daltons. Their small size explains why they are not inactivated by heat. ST causes an increase in cyclic GMP in host cell cytoplasm leading to the same effects as an increase in cAMP. STa is known to act by binding to a guanylate cyclase that is located on the apical membranes of host cells, thereby activating the enzyme. This leads to secretion of fluid and electrolytes resulting in diarrhoea.

This is in contrast to LT which has genetic homology to cholera toxin and DOES increase cAMP.

AMH.