To assessPseudomonasexotoxin A (ETA) compartmentalization, process-ing and cytotoxicity in vivo, we have studied the fate of internalized ETA with the use of thein vivo rodent liver model following toxin administra-tion, cell-free hepatic endosomes, and pure in vitro protease assays. ETA taken up into rat liver in vivo was rapidly associated with plasma mem-branes (5–30 min), internalized within endosomes (15–60 min), and later translocated into the cytosolic compartment (30–90 min).
