Heat-stable enterotoxin A yst YST-A ystA MKKIVFVLVLMLSSFGAFGQETVSGQFSDALSTPITAEVYKQACDPPLPPAEVSSDWDCCDVCCNPACAGC HSTA_YEREN Toxin which activates the particulate form of guanylate cyclase and increases cyclic GMP levels within the host intestinal epithelial cells. 71