Human Digestive Proteases:

The stomach serves to break large proteins into peptides. These peptides are then broken down into amino acids once they enter the duodenum.

• Pepsin = stomach

• Trypsin = duodenum

• Chymotrypsin

• Carboxypeptidase

Stomach

The stomach is the first point at which polypeptides are broken down. The low pH of the stomach causes enzymes to denature, opening them up to attack from proteases such as pepsin.

Pepsin

• Released by chief cells in the stomach.

• Expressed as a zymogen pepsinogen.

• Pepsinogen is converted to pepsin by HCl which is released by parietal cells of the stomach.

• Cleaves at the N-terminus after aromatic amino acids such as phenylalanine, tryptophan, and tyrosine.

• Optimum pH of 1.5 to 2. Pepsin denatures when the pH is more than 5.0.

If you want to see the effect of the protease pepsin, please enter the amino acid sequence of a polpeptide into the table below.

For example, why not try the sequence for phenylalanine hydroxylase (PAH); one of the enzymes that we are delivering to the GI tract.

Met S T A V L E N P G L G R K L S D F G Q E T S Y I E D N C N Q N G A I S L I F S L K E E V G A L A K V L R L F E E N D V N L T H I E S R P S R L K K D E Y E F F T H L D K R S L P A L T N I I K I L R H D I G A T V H E L S R D K K K D T V P W F P R T I Q E L D R F A N Q I L S Y G A E L D A D H P G F K D P V Y R A R R K Q F A D I A Y N Y R H G Q P I P R V E Y Met E E E K K T W G T V F K T L K S L Y K T H A C Y E Y N H I F P L L E K Y C G F H E D N I P Q L E D V S Q F L Q T C T G F R L R P V A G L L S S R D F L G G L A F R V F H C T Q Y I R H G S K P Met Y T P E P D I C H E L L G H V P L F S D R S F A Q F S Q E I G L A S L G A P D E Y I E K L A T I Y W F T V E F G L C K Q G D S I K A Y G A G L L S S F G E L Q Y C L S E K P K L L P L E L E K T A I Q N Y T V T E F Q P L Y Y V A E S F N D A K E K V R N F A A T I P R P F S V R Y D P Y T Q R I E V L D N T Q Q L K I L A D S I N S E I G I L C S A L Q K I K Stop