Intracellular assembly of human fibrinogen.

Hep-G2 cells, pulse-labeled with L-[35S]methionine, incorporate radioactivity within 2 min into precursor forms of fibrinogen and into fibrinogen. Pulse-labeled intracellular fibrinogen is first composed of radioactive B beta chains, followed by nascent A alpha chains. Radioactive gamma chains accumulate in the cells and later contribute, via intermediate forms, to the assembly of fibrinogen. Following a pulse-chase incubation with L-[35S]methionine, the radioactive composition of newly secreted fibrinogen also reflects the fact that there is a large intracellular pool of gamma chains.