Summary
The functional abnormality of Antithrombin III “Milano”, a previously described variant with monomeric and dimeric forms of abnormal AT III, has been further characterized. Affinity chromatography on heparin-Sepharose led to the separation and purification of two distinct tractions: fraction I is identical to normal AT III; fraction II (abnormal AT III) reproduces the abnormalities of the AT III “Milano”, i.e. lack of thrombin inhibition, incieased mobility by two-dimensional immunoclectrophoresis in the absence of heparin and migration as two bands with molecular weights of 60 K and 120 K by sodium dodecyl sulfate polyaeiylamide gel electrophoresis (SDS-PAGE). The interaction of both fiactions with purified u-thrombin was studied by the formation of complexes as well as by affinity chromatography on thrombin Seplmiose. No thrombin-AT III complexes could be demonstrated with either the monomeric or dimeric forms of purified variant AT III at both concentrations of thrombin used. Similarly, no binding to thrombin-Sepharose was observed, thus indicating that the molecular defect of AT III Milano is related to its absence of reactivity with thrombin.
Keywords
Antithrombin III - Variant - Thrombin binding site
