Biosynthesis of hepatocyte endoplasmic reticulum proteins

Abstract

Publisher Summary This chapter explores the application of rat hepatocyte that can serve as an excellent model for the study of the biosynthesis of endoplasmic reticulum (ER) membrane proteins. In the hepatocyte, as in all cell types, the biosynthetic machinery for the synthesis of secretory and membrane proteins includes both rough and smooth ER membrane-associated components, which affect a variety of co- and post-translational modifications of polypeptides synthesized in bound polysomes. Certain integral membrane proteins, such as cytochrome b 5 and NADH-cytochrome b 5 reductase, which are anchored to the membranes solely by a small carboxy terminal segment, are incorporated post-translationally into the ER membrane after their discharge from free polysomes into the cell sap. Other ER membrane proteins, however, only two of which have been demonstrated to be glycoproteins and to span the membrane, are synthesized in membrane-bound ribosomes and are inserted into the membrane during their synthesis. The fact that the concentrations of cytochrome b 5 and its reductase are much higher in the ER than in other membranes may reflect the affinity of these proteins for other components of the microsomal electron transport chains, such as those that are synthesized on bound polysomes.