STUDIES ON A PROTEOLYTIC ENZYME IN HUMAN PLASMA VIII. THE EFFECT OF CALCIU~ AND STRONTIUM IoNs ON Tm~ ACTIVATION OF THE PLASMA PROTEOLYTIC ENZYME* BY OSCAR D. RATNOFF,$ M.D. WITH THE TECHNICAL ASSISTANCE OF VELMA H. AXELROD AND ROSEMARY

The proteolytic enzyme in human plasma which is active at neutrality appears to exist in the circulating blood in the form of an inactive precursor. In vitro, the enzyme in clotted blood may become active "spontaneously" so that fibrinolysis occurs (1). This spontaneous activation is readily detectable in crude preparations of the enzyme (2), but is not observed when the enzyme is more highly purified (3). The conditions under which the proteolytic enzyme of the plasma becomes active have not been clarified. Scant attention has been paid to the effect of various ions on the process of activation. In the experiments to be described, the influence of various metallic ions was studied. I t was not possible to demonstrate that calcium or strontium altered the properties of activated plasma proteolytic enzyme. However, the activation of the enzyme from its precursor proceeded more rapidly in the presence of appreciable amounts of these cations. In the concentrations tested, other monovalent and bivalent cations did not accelerate activation. The effect of calcium ions was observed in crude preparations of the proteolytic enzyme, but was not apparent in solutions of more purified enzyme. Since the concentrations of calcium which were effective were comparable to those existing in the circulating blood, it seems possible that the phenomena observed may be significant in relation to the physiologic activation of the enzyme.