An Electrophoretic Study on the Effect of Heparin and Protamine Sulfate on the Interaction between Factor Xia and Antithrombin Iii

Abstract

It has been known that factor XIa (XIa) can react covalently with antithrombin III (ATIII) to form two complexes with ratios of 2ATIII:1XIa and 1ATIII:1XIa. In the hands of these investigators, the M.W.s, as measured by SDS-PAGE, were 265 kDa and 225 kDa, respectively. In this investigation it has been observed that the addition of 1 µg or 5 µg heparin (H) to 3.1 ϫ 10-5 (mol ATIII for 5 minutes prior to the addition of 1.125 µ 10-5 µmol XIa for a 30-minute incubation led to an increase in the 265 kDa band of 113% and 223%, respectively. These results were statistically significant (p < .01). However, when H was premixed with XIa first, before the addition of AT III, statistical increases in the 265 kDa band were also seen (267% and 183%, respectively; p < .0005, n = 6). Protamine sulfate (PS) statistically significantly (p < .05) inhibited the formation of the 265 and 225 kDa XIa-ATIII complexes at the 5 µg PS level when premixed with ATIII or XIa, respectively, the decreases in the 265 kDa band being 39.1 and 34.4%, respectively for [(ATIII/PS) + XIA] and [(XIa/PS) + ATIII] mixtures, and 23.1 and 23.8% for the 225 kDa band with [(ATIII/PS) + XIa] and [(XIa/PS) + ATIII] mixtures. These results with PS indicate that PS inhibits complex formation between XIa and ATIII at the 2ATIII:1 XIa and 1ATIII:1 XIa levels, in contrast with its reported stimulation of complex formation between thrombin and ATIII.