SOME FUNCTIONAL-PROPERTIES OF TELEOST ANTITHROMBIN

Antithrombin from bony fish (Teleostei), represented by an ancient sal monid, Atlantic salmon (Salmo salar L.), and a more evolved species fr om the same family, rainbow trout (Oncorhychus mykiss Walbaum), functi ons in vitro as does its human counterpart: it inactivates thrombin al most instantaneously in the presence of heparin and only slowly when h eparin is absent. The inhibitory activity of salmonid antithrombin tow ards the homologous thrombin did not differ noticeably from its inacti vating capacity in heterologous (teleost) systems, and enzyme-inhibito r reactions between reagents from fish and man proceeded just as effic iently. In all enzyme-inhibitor reactions with salmonid thrombin the i nactivation by salmonid antithrombin or diluted fish plasma was maxima l at pH 7.8 - 8.4. The inactivation was clearly dependent on heparin i n all systems and maximal at concentrations between 1.5 and 6 U/ml. Wh at particularly distinguishes the salmonid thrombin-antithrombin inter action from the human one is that the former has to function over a wi de range of temperatures. And the thrombin inactivating capacity of pu rified antithrombin and diluted plasma in the presence of heparin was indeed present at temperatures down to 3 degrees C, a capacity that hu man antithrombin also has retained. Even more interesting was that the teleost enzyme-inhibitor reaction was nearly independent of temperatu re under the conditions studied.