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Biomedical subjects

S Lopaciuk

Publications and source records attributed to S Lopaciuk.

At least 55 records · Page 3Linked to original sources
PubMed1980

Effects of neutral proteases from human leukocytes on structure and biological properties of human factor VIII.

Human factor VIII was purified from cryoprecipitate and incubated for up to 24 hours with four neutral proteases of human blood leukocytes, namely, with elastase-like protease (ELP), chymotrypsin-like protease (CLP), collagenase and gelatinase. Electrophoretic patterns showed a reproducible sequence of degradation of factor VIII and of its 230,000 molecular weight subunit by ELP and CLP. Intermediate products were similar but those resulting from exhaustive proteolysis by ELP and CLP differed distinctly from each other. Procoagulant activity of factor VIII was rapidly and completely destroyed by ELP and CLP before visible electrophoretic changes would be detected. No increase in this activity was observed prior to its destruction. Von Willebrand factor (ristocetin cofactor) activity was considerably more resistant to ELP and CLP and declined in rough relation to degradation of highly aggregated forms of factor VIII. ELP and CLP produced a pronounced progressive increase in the Laurell reaction antigen. Normal human plasma showed a high potency to inhibit ELP and CLP. Large doses of these enzymes (300 microgram per ml) produced in the plasma medium only a moderate fall in factor VIII procoagulant activity. Collagenase and gelatinase did neither degrade factor VIII nor change its biological properties.

Electrophoresis, Polyacrylamide Gel↗
PubMed1978

Assessment of plasma fibrinolytic system with use of chromogenic substrate.

A block of tests employing a chromogenic substrate H-D-Val-Leu-Lys-pNA (S-2251, Kabi AB, Stockholm) is proposed for a quantitative assessment of the plasma fibrinolytic system. It allows measurement of spontaneous plasmin activity, plasminogen content, activator activity (ability of plasma to activate plasminogen), immediate and progressive antiplasmin levels and alpha2-macroglobulin. All these assays could be performed within 45 min using a total of 0.4 ml of plasmin.

Fibrinolysin↗
PubMed1978

Difference between type I autoimmune inhibitors of fibrin stabilization in two patients with severe hemorrhagic disorder.

Inhibitors of fibrin stabilization of apparently autoimmune origin, found in two severely bleeding unrelated patients (W. G. and G. A.), were compared with regard to their biological target specificities, potencies and immunological characteristics. Both interfered only with the activation of fibrin stabilizing factor (coagulation Factor XIII) and, while totally preventing the conversion of this zymogen to the functional transamidating enzyme, fibrinoligase (Factor XIII(a)), they showed very little inhibition toward the enzyme itself. Thus, according to the classification of Lorand concerning biological specificities, both can be characterized as Type I inhibitors of fibrin stabilization. Potencies of the two inhibitors were quite similar when measured in conjunction with the plasma zymogen, but they differed remarkably in tests with platelet Factor 13. The inhibitor of patient W. G. prevented the activation of the zymogen from platelets, but that of G. A. had no effect on the platelet factor. It may therefore be concluded that the inhibitor of W. G. is directed exclusively against the a subunit which is a common constituent of plasma as well as platelet factors. The inhibitor of G. A., however, must be targeted against determinants uniquely characteristic for the ab ensemble of the plasma zymogen including the b subunit. On the basis of this difference in target specificity, the inhibitor of W. G. is designated as Type I-1 and that of G. A. as Type I-2. The inhibitors of both patients were isolated as immunoglobulins, and neutralization tests revealed that the antibody of W. G. comprised mainly heavy chains of the IgG1 and light chains of the kappa class. The antibody of G. A. proved to be considerably more heterogeneous and contained IgG1 and IgG3 heavy chains as well as kappa- and lambda-light chains. The finding that the antibody of W. G. inhibited conversion of platelet Factor 13 and also its thrombinmodified form, but had no effect on the thrombin and Ca(2+)-activated factor, is an indication that antigenic determinants existing both on the native zymogen and on its hydrolytically modified form become buried in the Ca(2+)-dependent step of activation. This is clear evidence for the occurrence of a significant conformational change in the protein structure attendant to the process of unmasking of its enzymic activity.

Adolescent↗
PubMed1975

Separation of human antihemophilic factor (AHF, factor VIII) from fibrinogen by means of defibrase.

Various attempts have been made in the past to remove fibrinogen from plasma fractions rich in factor VIII. Present studies indicated the Defibrase, a preparation of a thrombin-like enzyme from the venom of Bothrops atrox, might be successfully employed for this purpose. Addition of Defibrase to plasma or low-purity factor VIII concentrates allows for the complete removal of fibrinogen without any apparent reduction in the activity. It was also shown that treatment with Defibrase neither decreases the stability of factor VIII nor apparently affects its antigens properties.

Batroxobin↗