INTERACTIONS OF PLASMINOGEN AND FIBRINOGEN WITH MODEL SILICA GLASS SURFACES - ADSORPTION FROM PLASMA AND ENZYMATIC-ACTIVITY STUDIES

The adsorption of fibrinogen and plasminogen from plasma to silica gla ss, sulfonated silica glass, and lysine-derivatized silica glass has b een investigated. The data indicate that the sulfonated material has a high affinity for both fibrinogen and plasminogen, but that the ratio of plasminogen to fibrinogen is greater on the lysine-derivatized sur face. The adsorption data also suggest plasminogen as a possible contr ibutor to the fibrinogen Vroman effect, whereby initially adsorbed fib rinogen is displaced from the surface. The plasmin activity of plasmin ogen adsorbed to the lysine-derivatized silica glass and its sulfonate d precursor was assessed by both a chromogenic substrate assay and a r adioimmunoassay for the plasmin cleavage product of fibrinogen, the B beta 1-42 peptide. The data indicate that 1) the adsorbed plasminogen is not inherently plasmin-like; 2) the enzymatic activity associated w ith the bound plasminogen is significantly enhanced on both surfaces i n the presence of activator; and 3) in the presence of activator, the plasmin activity per mole of bound plasminogen on the lysinized materi al is approximately a factor of two greater than on the sulfonated mat erial based on the chromogenic substrate assay, and a factor of four g reater based on the B beta 1-42 radioimmunoassay. The lysinized materi al thus exhibits several properties that are different from its sulfon ated precursor. It adsorbs more plasminogen relative to fibrinogen aft er the Vroman peak, and this adsorbed plasminogen appears to be in a c onformation that is more readily activated to plasmin. Once activated, the surface bound plasmin shows enhanced ability to cleave either a l ow molecular weight chromogenic substrate or a macromolecular substrat e. These properties appear to be directly related to lysine residues o n the surface and may be the result of specific conformational changes occurring when plasminogen engages its lysine binding sites. (C) 1994 John Wiley and Sons, Inc.