Protein Translocation across the Membrane of the Endoplasmic Reticulum
The translocation of proteins across membranes is a feature common to all cells. In eukaryotes several distinct membranes are endowed with this capacity. Certain proteins (largely secretory) are translocated across the membrane of the endoplasmic reticulum (ER), while others are translocated across the membrane of mitochondria, chloroplasts, or peroxisomes. An understanding of the phenomenon of protein translocation depends upon answering three major questions: (1) What determines whether a protein will remain in the cytoplasm or will be translocated across a membrane? (2) How are the proteins selected to cross a specific membrane (endoplasmic reticulum, mitochondrial, chloroplast, or peroxisomal)? (3) What is the mechanism by which the actual physical translocation across the membrane occurs? This latter aspect requires the transfer of large hydrophilic moieties through a hydrophobic membrane and is certainly the most difficult to understand in molecular terms.
KeywordsPolypeptide Trypsin Stein Sulfhydryl Stomatitis
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