Vampire Bat Salivary Plasminogen Activator Is Quiescent in Human Plasma in the Absence of Fibrin Unlike Human Tissue Plasminogen Activator

The vampire bat salivary plasminogen activator (Bat-PA) is a potent PA that exhibits remarkable selectivity toward fibrin-bound plasminogen (Gardell et al, J Biol Chem 256: 3568, 1989). Herein, we describe the activity of recombinant DNA-derived Bat-PA (rBat-PA) in a human plasma milieu. rBat-PA and recombinant human single-chain tissue plasminogen activator (rt-PA) are similarly efficacious at lysing plasma clots. In stark contrast to rt-PA, the addition of 250 nmol/L rBat-PA to plasma in the absence of a clot failed to deplete plasminogen, α2-antiplasmin and fibrinogen. The lytic activities exhibited by finger-domain minus Bat-PA (F rBat-PA) and finger and epidermal growth factor-like domains minus Bat-PA (FG rBat-PA) were less than rBat-PA, especially at low concentrations of PA; nevertheless, these truncated forms also possessed a strict requirement for a fibrin cofactor. The loss of PA activity following the addition of rBat-PA to plasma was slower than that observed when either rt-PA or two-chain rt-PA was added. The efficacy, fibrin selectivity, and decreased susceptibility to inactivation exhibited by rBat-PA in vitro in a human plasma milieu suggests that rBat-PA may be superior to rt-PA for the treatment of thrombotic complications.