Potential-mediated and time-controlled first order activation of factor XII (Hageman factor) adsorbed to carbon surfaces.

Direct potential-mediated and time-controlled activation of purified human factor XII (FXII) immobilized on carbon has been demonstrated. Initial experiments were required to find a procedure for characterizing the immobilization of FXII and its activated form, factor XIIa (FXIIa). After achieving saturation of the carbon surface with FXII, surface catalytic activities could be generated under negative potential conditions. Activities depended on the duration and amplitude of the polarization applied to the immobilized FXII. The activities thus electrochemically induced in the surface-bound FXII molecules were tested biologically in the presence of normal human plasma and FXII-deficient plasma. The shortening of the activated partial thromboplastin time test suggested identity of the catalytic activities with that of activated FXII molecules. The electrochemical activation mechanism was consistently analysed according to first-order kinetics. The apparent rate constants increased in the presence of zinc ions.