Evidence for multiple enzyme site involvement in the modulation of thrombin activity by products of prothrombin proteolysis

Kinetic evidence is presented for the interaction of prothrombin with sever al distinctive topological regions of the thrombin molecule. Modulations of thrombin catalytic activity on the protein substrates prothrombin and pret hrombin 1 are demonstrated that involve the fragment 1 and fragment 2 porti ons. The inhibitory effects are demonstrably non-competitive. In addition t o exhibiting non-competitive inhibition, fragment 2 is capable of enhancing proteolysis by thrombin; and therefore to react with a second region of th e enzyme. On the basis of the crystallographic studies of the complex betwe en fragment 2 and thrombin (Arni et ail., Biochemistry 32 (1992) 4727), thi s activating site is proposed to be associated with exosite II. The alloste ric switch between procoagulant and anticoagulant activities identified fro m studies by Di Cera (Dang et al., Proc. Natl. Acad. Sci USA 92 (1995) 5977 ) could be 'thrown' by a macromolecular effector that is generated during t hrombin formation - a plausible mechanism for switching that deserves furth er investigation. (C) 1998 Elsevier Science :B.V. All rights reserved.