Modulation of staphylokinase-dependent plasminogen activation by mono- anddivalent ions

The effect of several ions (Cl-, Na+, K+, Ca2+) on the rate of plasminogen (Pg) activation by recombinant staphylokinase (rSTA) is reported. Both mono valent and divalent ions affect the rate at which Pg is activated by rSTA, in a concentration-dependent manner (range 0-100 mM). In almost all cases, a decrease of the initial velocity of activation was observed. Cl- showed t he most striking inhibitory effect at low concentrations (64% at 10 mM). Ho wever, in the presence of a fibrin surface, this inhibition was attenuated to 38%. Surprisingly, 10 mM Ca2+ enhanced the Pg activation rate 21% when a polymerized fibrin matrix was present. These data support the idea that io ns can modulate the rate of Pg activation through a mechanism that may be a ssociated with changes in the molecular conformation of the zymogen. This e ffect is strongly dependent on the presence of a fibrin clot.