Summary
The lysis time method for the determination of plasminogen has been investigated using
plasminogen-free thrombin and fibrinogen preparations.
The experiments have shown that the lysis of a fibrin clot is the result of two consecutive
reactions: the formation of fibrin which proceeds as a first order reaction and the
degradation of fibrin which proceeds as a zero order reaction. Plasminogen is activated
in a separate reaction. If the rate of the fibrin formation is much greater than the
rate of degradation, the lysis of the fibrin clot is approximately of zero order in
fibrin. The lysis time will then be inversely proportional to the plasmin concentration
and proportional to the fibrinogen concentration. In a double logaritmic system the
correlation between lysis time and plasmin activity is a straight line with a slope
of 135°.
Plasminogen is rapidly activated with streptokinase. Maximal activation is obtained
only with a certain streptokinase concentration. Higher concentrations inactivate
plasmin and with lower concentrations, the maximal activity is never reached. A spontaneous
inactivation is seen after about 30 minutes. With urokinase, a higher maximal plasminogen
activity is obtained than with streptokinase. Urokinase in higher concentrations does
not inactivate plasmin.
A standard assay for determination of plasminogen by the lysis time method has been
worked out and is based on these results.
