The processing and assembly of rat liver MAO
In eukaryotic cells enzymes are specifically compartmentalized either in intracellular membranes or in the spaces enclosed by these membranes. While the processes involved in the distribution of proteins to one organelle as opposed to another are still largely unknown, attempts have been made to explain the intracellular movement of proteins in the light of the “signal hypothesis” for the association of secreted proteins with the endoplasmic reticulum of secretory cells (1, 2). According to the most common formulation of this hypothesis, short tracts of amino acids at the amino-terminus of the nascent peptide chain direct the growing polypeptide to the endoplasmic reticulum. The still active polysomes then bind to the membranes where they complete the synthesis of the protein and cause its insertion into the lumen of the endoplasmic reticulum in a more or less concerted fasion (“vectorial synthesis”). Under normal circumstances, the short tract at the amino-terminus (“signal”) is cleaved by a protease in the lumen; however, by using an in vitro protein synthesizing system, secretory proteins that still retain their signal can by synthesized (“pre-forms”).
KeywordsMigration Electrophoresis Polypeptide Trypsin Monoamine
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