Studies of the plasmin system. I. Measurement of human and animal plasminogen; measurement of an activator in human serum.

A general assay method involving casein digestion is shown to be applicable for determination of several components of the plasmin system. Total plasminogen of human serum can be measured by use of sufficient streptokinase for instantaneous activation, accompanied by protection of the active plasmin with casein. Total plasminogen of guinea pig serum can be measured after complete activation with streptokinase in combination with human activator. The activator principle in whole human serum can be measured by its ability to activate guinea pig plasminogen.