The figure shows the combined presence of the peptidase and the transporter in the brush-border membrane of the intestine.

Protein forms about 20% of our nutrition. In the stomach and intestine protein is digested into smaller peptides through enzymes secreted by the pancreas. Subsequently, these peptides are further digested into amino acids, di- and tripeptides. These three compounds are then removed by transport proteins located in epithelial cells that line the intestine.

To optimize absorption, epithelial cells have finger-like extensions (villi) that enlarge the surface facing the lumen of the intestine, forming a brush-border membrane. The brush-border of intestinal cells is endowed with transporters and peptidases to ensure efficient digestion. We have now demonstrated that a transporter for amino acids and a peptidase form an assembly line to digest protein.

In the rare inherited condition Hartnup disorder digestion of proteins is impaired causing selective malnutrition of some amino acids. We found that certain mutations in Hartnup disorder affect the formation of this assembly line in the intestine.

Further Info Online:

• http://info.anu.edu.au/ovc/Media/Media_Releases/_2008/_April/_20080429_protein.asp
• http://www.fasebj.org/cgi/content/abstract/fj.08-107300v1