SIMULTANEOUS ADSORPTION OF FIBRINOGEN AND KININOGEN AT A SILICA SOLUTION INTERFACE/

The competitive adsorption of fibrinogen and high molecular weight kin inogen at different flow rates on silica capillaries has been studied at 37 degrees C in Tris buffer (Tris 0.05 M; NaCl 0.10 M) and at a dil ution of 10(-2) with respect to the plasma concentrations. By radiolab eling (I-125 and I-131) each protein differently, it is possible to fo llow the adsorption of both molecules from the mixture simultaneously. An accumulation of both proteins at the interface followed by a progr essive release of fibrinogen was observed. This release was not necess arily associated with an increase of the kininogen interfacial concent ration. From an analysis of the initial kinetics of adsorption of kini nogen vs wall shear rate, the diffusion coefficient (D approximate to 4.4 x 10(-7) cm(2) s(-1)) and the adsorption constant (K-a approximate to 2.4 x 10(-4) cm s(-1)) have been derived. The final adsorption kin etics of kininogen in the presence of fibrinogen is more compatible wi th a site adsorption model than with a random sequential adsorption mo del and leads to a much smaller adsorption constant, of the order of 1 0(-5) cm s(-1). This suggests that kininogen does not interact directl y with the bare silica but; with fibrinogen molecules, which act as ad sorption sites. For the molecular ratio of proteins in solution used h ere, it was found that the interfacial concentrations of both proteins are independent of shear rates at the maximum of fibrinogen concentra tion (0.4 mu g cm(-2) for fibrinogen (Fib) and 0.1 mu g cm(-2) for kin inogen (HK)), although appearing at varying times. These concentration s correspond to a molecular ratio HK/Fib of 0.9, which is close to an equimolecular composition at the interface. However at the beginning o f the adsorption process, we measured one molecule of kininogen for 10 molecules of fibrinogen at the surface, in accordance with a theoreti cal estimation from the solution concentrations and molecular masses.