Thrombin and albumin adsorption to PVA and heparin–PVA hydrogels. I. Single protein isotherms

More radiolabeled thrombin was adsorbed to heparin-polyvinyl alcohol (PVA) than to PVA, consistent with a specific interaction with the immobilized heparin. The maximum surface concentration on heparin-PVA was estimated to be approximately 450 nmol/m2 with an apparent affinity constant (Ka) of 2.5 microM-1; on PVA, the plateau concentration was 10 nmol/m2 with a Ka less than 1 nM-1. There was little difference in bovine serum albumin (BSA) adsorption between PVA and heparin-PVA. Interestingly, thrombin adsorption to polyethylene was indistinguishable from that to PVA despite the large difference in surface chemistry. BSA adsorbed to polyethylene with higher affinity than to the hydrogels, although the plateau concentrations were comparable. The adsorbed thrombin was biologically inactive at least towards chromogenic substrate, with the residual activity on PVA unaffected by subsequent incubations with antithrombin III. PVA and heparin-PVA presented a heterogeneous and complex substrate for interaction with proteins. The adsorbed protein was likely present in multiple states depending on the groups with which it interacted.