On the affinity between the plasminogen activator inhibitor type 2 and apolipoprotein A₁

Abstract

The plasminogen activator inhibitor type 2 (PAI-2) is present in its high molecular weight, glycosylated form in pregnancy plasma. When the protein was purified from retroplacental blood by immunoaffiity chromatography on a PAI-2 anti body column and the retained material was further fractionated by gel filtration chromatography, it was always contaminated by apolipoprotein A_l, the latter protein being identified by its N-terminal sequence, molecular weight in SDS-PAGE and immunological properties. The co-purification of the two proteins seemed to indicate a strong affinity between them, suggesting apolipoprotein A₁ to be a carrier protein for this PAI-2 form. Further investigation to check this hypothesis showed that the binding of apolipoprotein A₁ to the immunoaffinity support was PAI-2-independent and caused by a general surface affiity. This finding was corroborated by a study of the microtitre plate binding properties of the proteins. Pure, high molecular weight PA1 2 did not bind to apolipoprotein A₁-_-coated wells, but the latter protein bound to coated as well as to uncoated wells. Thus, there is no evidence for a specific binding between the two proteins.

Key Words:

• apolipoprotein A₁
• plasminogen activator inhibitor
• affinity