| Popis: |
Highly purified acrosin (A), the serine protease of the acrosome; which facilitates penetration of sperm through the zona pellucida, rapidly hydrolyzes tri- and tetrapeptide synthetic substrates relatively specific for thrombin (T) (S2238, chromozym TH, S2160) and factor Xa (Xa) (S2222) but only minimally hydrolyzes plasmin and plasma kallikrein substrates. A shares other biological properties with T and Xa. A slowly converts highly purified fibrinogen to fibrin and rapidly converts purified bovine prothrombin into T in a factor V or phospholipid-independent fashion. A, like T and Xa, is inhibited by antithrombin Ill; the inhibition is enhanced by heparin. A, like T, is inhibited by the pancreatic secretory trypsin inhibitor of Kazal but not by the Kunitz-Northrop trypsin inhibitor. A, unlike T, is not inhibited by hirudin and does not aggregate platelets. As has been reported for T and other serine proteases, A stimulates the growth of cultured fibroblasts in a concentration-dependent fashion. In T3T mouse fib,Vblasts only A stimulated DNA synthesis; T, plasmin and trypsin had no effect. Although the evolutionary and physiologic implications of similarities between A and clotting serine proteases remain unclear, the observed effect of A on cell proliferation may assign a new role for this enzyme in early embryogenesis. |
