143 Antiplasmin and plasminogen on STA and STA Compact, evaluated

Abstract

A new plasmin specific chromogenic tripeptide substrate (Tos-gly-pro-lys-pNA.HCl) has been used to study plasmin inhibition with human plasma and plasma samples fractionated by Sephadex G-150 gel filtration. “Immediate”, “fast-reacting” and “total” antiplasmin activities were determined in both “rate” and “endpoint” assays. The major “immediate” plasmin inhibitor was α2-antiplasmin with α2-macroglobulin exhibiting some “immediate” antiplasmin activity. Inhibition by α2-macroglobulin was markedly increased following incubation with plasmin for 30 seconds (“fast-reacting” inhibition) and 5 minutes (“total” inhibition), whilst inhibition by the α2-antiplasmin containing fractions was only slightly increased. Fractions containing α2-macroglobulin, α2-antiplasmin C1-esterase inhibitor, antithrombin III or α1-antitrypsin gave inhibition in the “total” inhibition assay. When a small amount of plasmin was added to a plasma sample and the mixture immediately fractionated by gel filtration, a plasmin-α2-macroglobulin complex with amidolytic activity was detected. These results confirm that α2-antiplasmin is the major plasma antiplasmin and suggest that α2-macroglobulin binds some plasmin even in the presence of α2-antiplasmin.