... secreted from the cell or localized to the ER lumen, and membrane proteins, such as those in the plasma membrane or inother organelles of the secretory pathway. Solubleproteins cross the membrane ... pumps.During the synthesis of a multi-spanning membrane protein, the seal would be provided in an alternatingmanner by either the nascent chain in the pore or,once the chain has left the pore, by the ... in the biosynthesis of many eukaryotic proteins is their par-tial or complete translocation across the endoplasmic reticulum membrane. A similar process occurs in prokaryotes, except that proteins...