Textilinins from Pseudonaja textilis textilis. Characterization of two plasmin inhibitors that reduce bleeding in an animal model

The incidence of vein-graft occlusion associated with myocardial infarction and thrombosis following the use of the plasmin inhibitor, aprotinin, to r educe blood loss during vascular surgery has prompted the isolation of an a lternative kinetically distinct inhibitor of plasmin from the venom of Pseu donaja textilis. This inhibitor has been called textilinin (Txln) and two d istinct forms have been isolated from the Brown-snake venom (molecular weig ht, 6688 and 6692). A comparison of plasmin inhibitor constants for aprotin in and the Txlns 1 and 2 indicated that the former bound very tightly (inhi bitor constant, K-i approximate to 10(-11) mol/l), while both of the latter bound less tightly (K-i approximate to 10(-9) mol/l). Homogeneity of Txlns 1 and 2 was confirmed by sodium dodecyl sulphate-polyacrylamide gel electr ophoresis and mass spectrometry. A sequence difference of six amino acids w as observed between the two forms of Txln. Txln 1 and 2 showed, respectivel y, 45 and 43% homology with aprotinin, while there was 58 and 55% homology, respectively, with a plasmin inhibitor from the venom of eastern Taipan, O xyuranus scurellatus. Both Txlns have six cysteines, like other inhibitors of this group, and homology was determined by alignment of these cysteines. Both have been shown to reduce blood loss by about 60% in a murine tail ve in bleeding model. It is proposed that the kinetic profiles of Txln 1 and 2 for plasmin allow the arrest of haemorrhage without the possible threat of thrombosis. Blood Coagul Fibrinolysis 11:385-393 (C) 2000 Lippincott Willi ams & Wilkins.