Isoelectric focusing pattern of human antithrombin III (AT‐III): Effects of heparin or thrombin on a microheterogeneous form of AT‐III

Abstract

AbstractAfter agarose gel isoelectric focusing (AGIEF) and immunofixation, human antithrombin III (AT‐III) in plasma showed a microheterogeneous pattern which consisted of 5 major and 5 minor components with isoelectric points (pI) between pH 4.8 and 5.2. Treatment with neuraminidase reduced this microheterogeneity of AT‐III to 1 major, 3 sub‐major and 2 or 3 minor components with a shift in pI to between pH 5.5 and 5.8. Thus, differential sialylation of the isoproteins partially contributed to the microheterogeneity observed. The addition of heparin to plasma produced broad acidic precipitates with pIs between pH 4.2 and 4.7 on the gel. The same acidic precipitates were also obtained from heparin‐purified AT‐III mixture. The appearance of these precipitates was related to the decreasing in number or in staining intensity of the native AT‐III bands. These precipitates may be complexes of heparin and AT‐III. The addition of human or bovine thrombin to plasma produced several basic minor components, which were similar to those in serum, at a thrombin concentration of 48 or more NIH U/ml‐plasma. The basic minor components were not obtained from a purified AT‐III‐thrombin mixture. These might be complexes between AT‐III, thrombin and some of the other coagulation factors.