MYOSIN AS COFACTOR AND SUBSTRATE IN FIBRINOLYSIS

Myosin accelerates plasminogen activation by tissue-type plasminogen a ctivator (tPA), and is degraded extensively by plasmin, Myosin binds b oth tPA and plasminogen, and enhances activation of des(1-77)-plasmino gen by tPA but not by urokinase-type plasminogen activator (uPA), Myos in decreases K-M and increases k(cat) for des(1-77)-plasminogen activa tion by tPA, to yield catalytic efficiencies in excess of 8000 M-1 s(- 1), The effect of myosin is attributed to its C-terminal portion, the myosin rod. With a K-M of 3 mu M, myosin is a high-affinity substrate for plasmin, The findings indicate that myosin is a cofactor for plasm inogen activation and a substrate for plasmin. (C) 1997 Federation of European Biochemical Societies.