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Related Concept Videos

Receptor-mediated Endocytosis01:38

Receptor-mediated Endocytosis

Overview
Receptor-mediated Endocytosis01:20

Receptor-mediated Endocytosis

Receptor-mediated endocytosis is when bulk amounts of specific molecules are imported into a cell after binding to cell surface receptors. The molecules bound to these receptors are taken into the cell through inward folding of the cell surface membrane, which is eventually pinched off into a vesicle within the cell. Structural proteins, such as clathrin, coat the budding vesicle.
Clathrin-Mediated Endocytosis of LDL
One well-characterized example of receptor-mediated endocytosis is the...
Insulin Secretory Vesicles01:05

Insulin Secretory Vesicles

Insulin secretory vesicles release insulin to stimulate blood glucose uptake and regulate carbohydrate metabolism. When the blood glucose levels increase, glucose enters the pancreatic β-islet cells through glucose transporters. Once inside, glucose is metabolized through glycolysis, the citric acid cycle, and the electron transport chain, producing ATP. This increase in ATP concentration closes ATP-sensitive potassium channels, leading to depolarization of the membrane and the opening of...
Glucose Homeostasis: Pancreatic Islets and Insulin Secretion01:27

Glucose Homeostasis: Pancreatic Islets and Insulin Secretion

The pancreatic islets comprising only 1%-2% of the volume are highly vascularized and innervated mini-organs. They contain five endocrine cell types, including β cells that secrete insulin, which is synthesized as a single polypeptide chain, preproinsulin, processed to proinsulin, and finally to insulin and C-peptide. This process is complex and regulated, involving the Golgi complex, the endoplasmic reticulum, and the secretory granules of the β cell.
Insulin and C-peptide are co-secreted in...
Insulin: The Receptor and Signaling Pathways01:28

Insulin: The Receptor and Signaling Pathways

Insulin action is mediated through a receptor tyrosine kinase, akin to the IGF-1 receptor. The number of receptors per cell varies significantly, from 40 on erythrocytes to 300,000 on adipocytes and hepatocytes. The insulin receptor consists of linked α/β subunit dimers, forming a heterotetramer glycoprotein with two extracellular α subunits and two β subunits spanning the membrane. The α subunits inhibit the inherent tyrosine kinase activity of the β subunits, but this inhibition is released...
Insulin: Biosynthesis, Chemistry, and Preparation01:25

Insulin: Biosynthesis, Chemistry, and Preparation

The endoplasmic reticulum (ER) of pancreatic β-cells synthesizes preproinsulin, which consists of a signal peptide, A and B chains, and a C-peptide. Preproinsulin is then cleaved and folded into proinsulin, which translocates to the Golgi apparatus for sorting and packaging into secretory granules. In these granules, enzymatic clipping generates insulin and C-peptide.
Damage or functional impairment of β-cells inhibits insulin production, leading to diabetes. Diabetes treatment primarily uses...

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Related Experiment Video

Updated: Jul 13, 2026

Coculture Analysis of Extracellular Protein Interactions Affecting Insulin Secretion by Pancreatic Beta Cells
05:51

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Published on: June 15, 2013

Cellular internalization of proinsulin C-peptide.

E Lindahl1, U Nyman, E Melles

  • 1Department of Medical Biochemistry and Biophysics (MBB), Karolinska Institutet, 171 77, Stockholm, Sweden.

Cellular and Molecular Life Sciences : CMLS
|February 7, 2007
PubMed
Summary

Proinsulin C-peptide is internalized into cells via an energy-dependent pathway. This peptide hormone may have further intracellular actions, suggesting a novel intracrine function.

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Area of Science:

  • Cell Biology
  • Endocrinology
  • Molecular Biology

Background:

  • Proinsulin C-peptide binds cell membranes and has intracellular effects.
  • Cellular internalization of C-peptide has not been previously demonstrated.

Purpose of the Study:

  • To investigate the internalization of proinsulin C-peptide in target cells.
  • To determine the mechanism and intracellular localization of C-peptide.

Main Methods:

  • Confocal microscopy using immunostained or rhodamine-labeled C-peptide.
  • Cellular uptake studies at varying temperatures (37°C vs. 4°C) and with pertussis toxin.
  • Surface plasmon resonance to identify intracellular binding proteins.

Main Results:

  • C-peptide is internalized into the cytosol of Swiss 3T3 and HEK-293 cells.
  • Nuclear transport of C-peptide was observed.
  • Internalization is energy-dependent, pertussis toxin-sensitive, and occurs without rapid degradation.
  • Intracellular proteins bind to C-peptide.

Conclusions:

  • C-peptide internalization occurs via a specific, regulated mechanism.
  • The data support C-peptide acting as an intracrine peptide hormone.
  • C-peptide may possess additional intracellular sites of action.