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Absorption of Proteins as Dipeptides, Tripeptides, or Amino Acids

المؤلف:  John E. Hall, PhD

المصدر:  Guyton and Hall Textbook of Medical Physiology

الجزء والصفحة:  13th Edition , p841

2026-10-19

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As explained earlier, most proteins, after digestion, are absorbed through the luminal membranes of the intestinal epithelial cells in the form of dipeptides, tripeptides, and a few free amino acids. The energy for most of this transport is supplied by a sodium co-transport mechanism in the same way that sodium co-transport of glucose occurs. That is, most peptide or amino acid molecules bind in the cell’s microvillus membrane with a specific transport protein that requires sodium binding before transport can occur. After binding, the sodium ion then moves down its electrochemical gradient to the interior of the cell and pulls the amino acid or peptide along with it. This process is called co-transport (or secondary active transport) of the amino acids and peptides (see Figure 1). A few amino acids do not require this sodium co-transport mechanism but instead are transported by special membrane transport proteins in the same way that fructose is transported, by facilitated diffusion.

Fig1. Absorption of sodium, chloride, glucose, and amino  acids through the intestinal epithelium. Note also osmotic absorption of water (i.e., water “follows” sodium through the epithelial  membrane). 

At least five types of transport proteins for amino acids and peptides have been found in the luminal membranes of intestinal epithelial cells. This multiplicity of transport proteins is required because of the diverse binding properties of different amino acids and peptides.