Summary
1. Improvements in preparations of tissue activator and plasminogen and termination
of activation by epsilon aminocaproic acid have permitted the use of a quantitative
caseinolytic assay for the measurement of the plasmin formed. The following data indicate
that the activation of plasminogen by tissue activator is catalytic :
a) Biphasic curve obtained when velocity was plotted against plasminogen concentration.
b) First order kinetics.
c) Dependence of the turnover number on tissue activator concentration.
2. The temperature and pH stability of tissue activator were similar to those reported
for urokinase. Since both of these enzymes have now been shown to activate plasminogen
by a catalytic mechanism, these data support the suggestion that urokinase may be
an excretory form of tissue activator which has been released into the circulation.