Interaction between proteases and bovine erythrocyte membranes. II. Binding of fibrinolytic components

Abstract

Abstract 1. 1. Bovine erythrocyte ghosts bind plasminogen and plasmin, but do not inhibit the caseinolytic activity of plasmin. 2. 2. Urokinase, which is not bound to ghosts, readily activates plasminogen in the presence and absence of ghosts without an apparent loss in efficiency. 3. 3. Inactivation of trypsin solutions at physiological pH is prevented by the presence of ghosts having the capacity to bind the enzyme. 4. 4. Incomplete activation of plasminogen by trypsin is observed upon addition of trypsin to ghosts-plasminogen mixtures or upon addition of plasminogen to ghosts-trypsin mixtures. 5. 5. Increased binding of [ 3 H]trypsin to ghosts is seen in the presence of plasminogen regardless of the order of addition of the proteins to the ghosts, suggesting that there are separate binding sites on the surface of the membranes for trypsin and plasminogen, and that trypsin might be bound both directly to ghosts and to plasminogen which bind to ghosts. 6. 6. Totally acetylatated trypsin incompletely activates plasminogen in the presence of ghosts in a manner identical to that of trypsin. These results are interpreted to suggest that acetylated sites on trypsin, which reduce binding directly to ghosts, are in no way influential in plasminogen activation, and that the binding of plasminogen to ghosts must be the step which, in an unknown manner, affects conformation of the former thereby reducing the efficiency of native trypsin and acetyltrypsin, while exerting no noticeable influence on urokinase activation. 7. 7. A potential role for the possible transport by membranes of zymogens and enzymes involved in fibrinolysis in the blood is suggested.