Release of B beta peptides from fibrinogen or fibrin in the presence of alpha 2 antiplasmin.

When Glu-plasminogen (plg) was activated by urokinase (UK) in the presence of fibrinogen or fibrin, B beta peptides (B beta 1-42) were released faster from fibrinogen than from fibrin (B beta 15-42). These results were contrary to faster release of B beta 15-42 from fibrin in the UK-activated clotted plasma in comparison to the release of B beta 1-42 from UK-activated plasma. The addition of plasma or lysine-Sepharose pass through fraction to the above system resulted in faster release of B beta peptides from fibrin than fibrinogen. The addition of alpha 2 antiplasmin (alpha 2AP) to the mixture of Glu-pig, UK and fibrinogen or fibrin resulted in faster release of B beta peptides from fibrin than from fibrinogen. These results indicate that fibrin protected plasmin from inactivation by alpha 2AP, leading to cleavage of Arg(42)-Ala(43) bond in beta-chain of fibrin which seems to be less susceptible to plasmin than the same bond in fibrinogen.