Analysis of phenotypic variation of human plasma antithrombin III by isoelectric focusing

Human plasma antithrombin III (AT III) shows heterogenous banding pattern by agarose gel isoelectric focusing (AGIEF) and its heterogeneity is considered to be closely related to the development of activity.Among 300 citrated plasma, 298 samples show the same AGIEF pattern (AT IIIc, c; common), however 2 of them exhibited the different pattern (AT IIIv, v; variant). AT IIIc consists of 5 major bands (pH 4.82-5.12) and the amount of band with isoelectric poit (pl) 4.87 accounts for 61.7% of total AT III. In contrast, AT IIIv shows 7 major bands (pH 4.76-5.12) and the bands with pl 4.84 and 4.87 account for 36 and 37%, respectively. Moreover, some bands of AT IIIv possess same pls as those of AT IIIc. After the treatment with neuraminidase, AT IIIc and AT IIIv decreased their heterogeneity to 1 major (pl=5.72) and 2 mayor (pl=5.60, 5.72) bands, respectively. From the analysis of AGIEF pattern of these AT III, AT IIIv was suggested to be phenotypically heterozygous and combination of the band-group of AT IIIc and variant bandgroup which have pH 0.12 lower than AT IIIc. AT IIIc and AT IIIv inhibited thrombin in a similar manner in the absence or the presence of excess heparin, However at lower heparin concentration, AT IIIv inhibits thrombin more slowly than AT IIIc.Through these studies it is concluded that the variant type of AT III detected by AGIEF represents a qualitative abnormality and that it is suspected to be responsible for the pathogenesis of thromboembolism.