Internalization of polypeptide hormones and receptor recycling |
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Authors: | J. -L. Carpentier P. Gorden A. Robert L. Orci |
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Affiliation: | (1) Institute of Histology and Embryology, University of Geneva Medical Center, CH-1211 Geneva 4, Switzerland;(2) Diabetes Branch, National Institute of Arthritis, Diabetes, and Digestive and Kidney Diseases, National Institutes of Health, 20205 Bethesda, Maryland, USA |
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Abstract: | Conclusion The insulin receptor is an integral protein of the plasma membrane of the cell. It is composed of two subunits: an subunit, which binds the hormone, and a subunit which is a tyrosine specific protein kinase capable of undergoing autophosphorylation. These independent subunits are synthesized by way of a higher molecular weight single chain precursor and thus are the product of a single gene29, 49, 85 localized to chromosome 1929, 91. Assuming that the insulin receptor is synthesized in the same fashion as other integral membrane glycoproteins, then the nucleus, the rough endoplasmic reticulum, and the Golgi apparatus are involved in its biosynthesis. Further, there must be some form of transport of the mature receptor subunits to the plasma membrane where they are inserted.By contrast, the endocytotic route involves coated pits, coated vesicles, large clear vesicles or endosomes, multivesicular bodies and other lysosomal forms. In addition, it is possible that some other as yet unidentified organelle is involved in recycling (fig. 8). At the present time, with respect to the insulin receptor, the biosynthetic pathway and the endocytotic pathway appear to be separate. Further, it does not appear that either pathway, i. e. synthesis or endocytosis, exerts a regulatory function over the other. |
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Keywords: | Insulin receptor receptor recycling endocytosis polypeptide hormone receptor regulation |
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