The plasma carboxypeptidases and the regulation of the plasminogen system

Central to the regulation of the plasminogen system, a proteolytic network that mediates degradation of fibrin and facilitates cell migration, is the binding of plasminogen to carboxy-terminal lysines. These residues occur either naturally on plasmin substrates or cell surfaces or are generated as a consequence of partial plasmin degradation. The basic carboxypeptidases of plasma are capable of removing such carboxy-terminal lysines. Carboxypeptidase N, which is constitutively active, suppresses plasminogen binding to cell surfaces; plasma carboxypeptidase B, which must be proteolytically activated, not only suppresses cellular binding of plasminogen but also dampens fibrinolysis. Thus, the plasma carboxypeptidases may constitute an important regulatory pathway for controlling the activity of the plasminogen system in physiologic, pathophysiologic, and pharmacologic circumstances. (Trends Cardiovasc Med 1997;7:71-75). © 1997, Elsevier Science Inc.