Proteolytic Activity of Guinea Pig Serum Activated by Streptokinase-Human Plasminogen Preparations

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Abstract
The incubation of guinea pig serum with a streptokinase-human plasminogen preparation (from purified plasminogen) activates a proteolytic enzyme in the guinea pig serum. Optimal conditions for activity, kinetics, Km values and heat stability of elements of this system were studied. The proteolytic activity of this system was strongly inhibited by lysine ethyl ester and p-toluenesulfonylarginine methyl ester, apparently in a competitive manner. Serum dilution activity curves suggest the presence in guinea pig serum of dissociable protease inhibitors. The proteolytic activity of human plasmin does not appear to be essential for the activation of guinea pig protease, as indicated by heat stability studies. Possible mechanisms of activation are discussed. A survey of other animal species showed the widespread presence of serum proteases which could be activated with streptokinase-human plasminogen mixtures. The human activator systems may prove to be a useful tool in experimental studies of the physiological significance of the protease system.