Purification and partial characterisation of alpha(2)-antiplasmin and plasmin(ogen) from ostrich plasma

Alpha2-Antiplasmin: The Devil You Don't Know in Cerebrovascular and Cardiovascular Disease

Alpha2-antiplasmin (α2AP), the fast-reacting, serine protease inhibitor (serpin) of plasmin, was originally thought to play a key role in protection against uncontrolled, plasmin-mediated proteolysis of coagulation factors and other molecules. However, studies of humans and mice with genetic deficiency of α2AP have expanded our understanding of this serpin, particularly in disease states. Epidemiology studies have shown an association between high α2AP levels and increased risk or poor outcome in cardiovascular diseases. Mechanistic studies in disease models indicate that α2AP stops the body's own fibrinolytic system from dissolving pathologic thrombi that cause venous thrombosis, pulmonary embolism, arterial thrombosis, and ischemic stroke. In addition, α2AP fosters the development of microvascular thrombosis and enhances matrix metalloproteinase-9 expression. Through these mechanisms and others, α2AP contributes to brain injury, hemorrhage and swelling in experimental ischemic stroke. Recent studies also show that α2AP is required for the development of stasis thrombosis by inhibiting the early activation of effective fibrinolysis. In this review, we will discuss the key role played by α2AP in controlling thrombosis and fibrinolysis and, we will consider its potential value as a therapeutic target in cardiovascular diseases and ischemic stroke.

Ostrich antithrombin III: kinetics and mechanism of inhibition of ostrich thrombin

A kinetic investigation of ostrich thrombin specificity, its regulation and evolutionary development in comparison to those of other well-characterised species may contribute to the understanding of the structure-function relationships of thrombin. Antithrombin III (ATIII) was purified from ostrich plasma by heparin-Sepharose and Super Q-650S chromatography. It exhibited a M(r) of 59.2K and a pI in the range of 5.2-6.0. The ostrich N-terminal sequence was compared to those of other known species and showed the highest identity with rabbit ATIII (31%). Inhibition studies included the interaction of ostrich and human ATIII with bovine, human and ostrich thrombin. At a 2:1 molar ratio of ostrich ATIII to enzyme, 20 and 40% remaining activity was found for bovine and ostrich thrombin, respectively. Ostrich thrombin exhibited a pH and temperature optimum of 9.0 and 60 degrees C, respectively. Hydrolysis of seven peptide p-nitroanilide substrates by ostrich thrombin revealed D-Phe-Pip-Arg-pNA (k(cat)/K(m)=9.65 microM(-1)s(-1)) as the substrate with the highest catalytic efficiency. The effect of monovalent cations on ostrich thrombin catalysis revealed enhanced activity with Na(+). The calculated K(i) values for the complex formation between ostrich thrombin and ostrich (9.29 x 10(-11)M) and human (9.66 x 10(-11)M) ATIII are comparable to reported results. The results obtained from the present study confirmed that ostrich thrombin and ATIII are closely related to the corresponding molecules of other species in terms of physicochemical and kinetic properties.