text: PT is released from B. pertussis in an inactive form. Following PT binding to a cell membrane receptor, it is taken up in an endosome, after which it undergoes retrograde transport to the trans-Golgi network and endoplasmic reticulum. At some point during this transport, the A subunit (or protomer) becomes activated, perhaps through the action of glutathione and ATP. PT catalyzes the ADP-ribosylation of the α subunits of the heterotrimeric G protein. This prevents the G proteins from interacting with G protein-coupled receptors on the cell membrane, thus interfering with intracellular communication. The Gi subunits remain locked in their GDP-bound, inactive state, thus unable to inhibit adenylate cyclase activity, leading to increased cellular concentrations of cAMP.
  Increased intracellular cAMP affects normal biological signaling. The toxin causes several systemic effects, among which is an increased release of insulin, causing hypoglycemia. Whether the effects of pertussis toxin are responsible for the paroxysmal cough remains unknown.
  As a result of this unique mechanism, PT has also become widely used as a biochemical tool to ADP-ribosylate GTP-binding proteins in the study of signal transduction. It has also become an essential component of new acellular vaccines.