Toxin which activates the particulate form of guanylate cyclase and increases cyclic GMP levels within the host intestinal epithelial cells. In cultured cells, expressed only at temperatures <30 degrees Celsius. Under conditions of high osmolarity and alkaline pH (as it is the case in the host's intestine), it is expressed at 37 degrees Celsius. Transcription reached a maximum at the entry to the stationary phase and significantly varied in different Y.enterocolitica strains. Belongs to the heat-stable enterotoxin family.