Plasminogen in the chick embryo. Transport and biosynthesis.

As part of a program to define potential roles for plasminogen activation during development, we have studied the metabolism of plasminogen in the chick embryo. Here we report that: 1) plasminogen is present in significant quantities in the yolk of fertile, unincubated eggs; 2) the zymogen can be translocated intact, from the yolk to the developing embryonic circulation; and 3) de novo synthesis of plasminogen occurs during the early phases of embryonic life. The combination of a reservoir of the zymogen in the yolk and protein biosynthesis thus ensures the availability of a substrate for enzymes which may participate in morphogenetic events occurring throughout embryonic life.