THE FIBRINOLYTIC PATHWAY OF HUMAN PLASMA : ISOLATION AND CHARACTERIZATION OF THE PLASMINOGEN PROACTIVATOR

The conversion of the plasminogen proactivator to plasminogen activator by activated Hageman factor or its fragments has been recognized as an essential step in the conversion of plasminogen to plasmin. The plasminogen proactivator has been completely separated from prekallikrein and pre-PTA, two other proenzyme substrates of activated Hageman factor or its fragments. Plasminogen proactivator, free of any contaminating proteins as assessed by disc gel electrophoresis or isoelectric focusing, revealed a single band with an isoelectric point of 8.9 corresponding in position to the Hageman factor activatable material eluted from replicate unstained gels. After conversion of plasminogen proactivator by Hageman factor fragments to the plasminogen activator, the active site of the plasminogen activator is not inhibited by C1INH and is thus readily distinguished from that of kallikrein or PTA. The plasminogen activator is susceptible to inactivation by DFP while the plasminogen proactivator is not, as has been the case for esterases having a serine in the active site. Its interaction with plasminogen is inhibited by ϵ-aminocaproic acid.