Endocytosis: biochemical analyses.
Many integral membrane proteins synthesized in the endoplasmic reticulum ultimately arrive at the cell surface to contact the cell environment. During transit through the Golgi and trans-Golgi network, proteins acquire post-translational modifications that can be used to track the appearance of such modified proteins at the cell surface. Cellular proteins can be treated with enzymes--e.g., sialidase or protease--or antibodies, or biotinylated to identify molecules that have reached the cell surface. Some proteins first enter the endocytic pathway before appearing at the cell surface; this is detected by treating the cells at 4 degrees and 37 degrees C. Analysis of the number of sialic acids on proteins of cells treated at 4 degrees C identifies proteins resident at the cell surface, while cells treated at 37 degrees C internalize the sialidase, which can then act with proteins in the endocytic compartments.
McGraw
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Weill Medical School of Cornell University, New York, New York, USA.
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D000818:Animals; D001671:Biochemistry / Q000379:methods*; D002478:Cells, Cultured; D004705:Endocytosis / Q000502:physiology*; D006801:Humans; D021381:Protein Transport / Q000502:physiology*