Maybe a way to remember this would be to think about Hartnup disease, an AR deficiency of neutral amino acid (primarily tryptophan is implicated) transporters in the proximal renal tubular cells and on ENTEROCYTES. This leads to neutral aminoaciduria and decreased absorption from the gut and little breakdown of dipeptides and tripeptides to amino acids in the intestinal mucosa. Decreased absorption from the gut causes decreased tryptophan for conversion to niacin and pellagra-like symptoms (diarrhea, dementia and hallucinations, and dermatitis in the C3-4 circumferential "broad collar" or "Casal necklace" dermatome, hyperpigmentation of sun-exposed limbs).
So if you can't convert dipeptides and tripeptides to amino acids in the ENTEROCYTES in the INTESTINAL MUCOSA, then you can get Hartnup disease.
submitted by โshak360(23)
Dipeptides and tripeptides are produced by the activity of trypsin and chymotrypsin within the lumen of the duodenum. Free amino acids are produced upon further digestion of these small peptides within the brush border of the intestinal mucosa.
The lumen of the duodenum is wrong because that is where larger complex polypeptides are broken down to di- and tripeptides but the action of taking di- and tripeptides down to individual amino acids happens in the intestinal mucosa.