SYNTHESIS OF PLASMA MEMBRANE OF LIVER CELL

The steps involved in the synthesis of a plasma (surface) membrane are completely unknown. For the newly-synthesized protein constituents of the membrane, four possibilities have been considered. First, newly-formed proteins are added directly to the membrane; second, they mix with a soluble pool and are then incorporated into the membrane; third, they are assembled into complex units that are then built into the membrance; and fourth, they are incorporated into a precursor membrance that is later converted into a plasma membrane. The work presented here shows that proteins may be formed several hours before they are built into the liver plasma membrane. Thus, a direct incorporation of all new protein can be ruled out. It is not yet possible, however, to distinguish among the remaining three possibilities. © 1968.