Inhibition of plasmin activity by α2-macroglobulin

159

A B S T R A C T This study demonstrates that human plasma a2-macroglobulin preparations possess an enzymic activity that degrades fibrinogen, resulting in the formation of products whose structure resembles that of circulating fibrinogen catabolites. The sequence of degradation is similar to that observed in plasmincatalyzed digests, in that Aa-chain fragmentation precedes that of B,8-chain. The addition of plasminogen activators to plasma induced an increase in the N-atosyl-L-arginine methyl ester HCl esterase and fibrinogenolytic activity associated with a2-macroglobulin purified from this plasma, indicating that the enzymic activity of the complex was preserved and could be increased in the presence of other plasma enzyme inhibitors. Immunochemical studies demonstrated that an a2-macroglobulin-plasmin complex had formed in urokinase-treated plasma. This a2-macroglobulin preparation manifested an esterolytic profile like that of a complex prepared from plasmin and purified a2-macroglobulin. After complex formation with a2-macroglobulin in plasma, plasmin retained less than 0.1% of its fibrinogenolytic activity. That plasmin expressed its activity while bound to a2-macroglobulin was suggested by immunoprecipitation of this activity with aa-macroglobulin antibody and by the demonstration that pancreatic trypsin inhibitor did not effectively inhibit its fibrinogenolytic or esterolytic activity. These results raise the possibility that, in addition to its activity as a major plasma proteolytic enzyme inhibitor, a2-macroglobulin may modThis paper was presented in part at the 15th Annual Meeting,

Section: Resultssupporting

confidence: 86%

Section: Resultsmentioning

confidence: 99%

Degradation of Human Fibrinogen by Plasma α2-Macroglobulin-Enzyme Complexes

Harpel¹,

Mosesson²

1973

159

“…C1 inactivator, purified from human serum, has been shown to inhibit kallikrein, plasma permeability factor (PF/dil), Cl, Hageman factor, plasma thromboplastin antecedent, and plasmin (31)(32)(33)(34). Plasma a2-macroglobulin inhibits kallikrein (27,34), plasmin (35,36), and thrombin (37) by binding with these enzymes and forming a high molecular weight complex. Trasylol is a kallikrein, plasmin and trypsin inhibitor purified from bovine tissues (38).…”

Section: Discussionmentioning

confidence: 99%

Studies on the Interaction between Collagen and a Plasma Kallikrein-Like Activity EVIDENCE FOR A SURFACE-ACTIVE ENZYME SYSTEM

Harpel¹

1972

A B S T R A C T This study has demonstrated that collagen particles, after exposure to platelet-poor human plasma and subsequent washing, generate a kinin-like agent when incubated with prekinin substrate. The binding of kinin-generating activity to collagen in the plasma collagen incubation mixture occurs rapidly, whereas the loss of this activity in the incubation mixture occurs relatively slowly. The Hageman factor appeared to be necessary for the surface-bound kiningenerating activity, as this activity was absent in collagen exposed to Hageman factor-deficient plasma. These studies have partially characterized the plasma-derived enzymatic activity bound to collagen. Incubation of collagen with plasma caused a concentration-dependent reduction in the kinin-producing activity which was generated by the addition of ellagic acid, a known activator of plasma kallikrein. The kinin-inducing activity bound to collagen is inhibited by soybean trypsin inhibitor, Trasylol, serum C1 inactivator and the plasma a2-macroglobulin, but not by lima bean trypsin inhibitor. An eluate prepared from plasma-treated collagen, when compared with purified plasma kallikrein, shared a similar inhibitor profile. Selective chemical blockage of the free carboxyl groups on the collagen molecule, or heat denaturation, inactivated the ability of the collagen to generate kinin-like activity after incubation with plasma. Removal of the collagen telopeptides or blockage of the free amino groups failed to affect the collagen-plasma interaction. The binding of This study was presented in part at the 44th Scientific

“…a2-Macroglobulin (a2M),' antithrombin III (ATIII), and al-proteinase inhibitor (a1-antitrypsin, a1PI) all are capable of inactivating Factor X. in vitro. a2M is unique in its ability to inhibit proteinases from all four classes (2), including the homologous serine proteinases thrombin and Factor Xa (3)(4)(5)(6)(7). ATIII only inhibits serine proteases such as thrombin and Factor X.…”

Section: Introductionmentioning

confidence: 99%

Regulation of factor Xa in vitro in human and mouse plasma and in vivo in mouse. Role of the endothelium and plasma proteinase inhibitors.

Fuchs¹,

Pizzo²

1983

A B S T R A C T The regulation of human Factor Xa was studied in vitro in human and mouse plasma, and in vivo in mouse. In human plasma, '251-Factor Xa bound to a1-proteinase inhibitor, antithrombin III, and a2-macroglobulin in a ratio of 4.9:1.9:1 as determined by gel electrophoresis and by adsorption to IgG-(antiproteinase inhibitor)-Sepharose beads. The distribution of Factor Xa in mouse plasma was similar. The clearance of Factor Xa in mice was rapid (50% clearance in 3 min) and biphasic. a1-Proteinase inhibitor-trypsin, even at a 2,000-fold molar excess, failed to inhibit the clearance of Factor Xa, while a2-macroglobulin-trypsin inhibited only the later phase of clearance. The plasma clearance of diisopropylphosphoryl-Factor Xa was more rapid than native Factor X. (50% clearance in 2.5 min), and the clearance was blocked by diisopropylphosphoryl-thrombin. Electrophoresis experiments confirmed that by 2 min after injection into the murine circulation, 90% of the bound Factor Xa was on a2-macroglobulin, in marked contrast to the in vitro results. Organ distribution studies at 3 and 15 min with 125I_ Factor X. demonstrated that the majority of radioactivity was in the liver, with significant radioactivity also present in lung and kidney. Autopsies performed 30 s after injection of 125I-Factor Xa also demonstrated significant binding to the aorta and vena cava. These studies indicate that Factor Xa binds to specific thrombin-binding sites on endothelial cells, and that this binding alters its proteinase inhibitor specificity. Factor Xa binds to a2-macroglobulin in vivo, whereas the predominant in vitro inhibitor of Factor X. is a,-proteinase inhibitor.