An ENTEROTOXIN from vibrio cholerae. It consists of two major protomers, the heavy (H) or A subunit and the B protomer which consists of 5 light (L) or B subunits. The catalytic A subunit is proteolytically cleaved into fragments A1 and A2. The A1 fragment is a MONO(ADP-ribose) TRANSFERASE. The B protomer binds cholera toxin to intestinal epithelial cells, and facilitates the uptake of the A1 fragment. The A1 catalyzed transfer of ADP-ribose to the alpha subunits of heterotrimeric G proteins activates the production of cyclic amp. Increased levels of cyclic amp are thought to modulate release of fluid and electrolytes from intestinal crypt cells.