Question

Pepsin is the name given to a mix of several digestive enzymes secreted by gland that line the stomach. These glands also secrete HCl, which dissolves the particulate matter in food, allowing pepsin to enzymatically cleave individual protein molecules. The resulting mixture of food, Hal, and digestive enzymes is known as chyme and has a pH near 1.5. What pI would you predict for the pepsin proteins? What functional groups must be present to confer the pI on pepsin? Which amino acids in the protons would contribute such groups?

Answer 1

Pepsin is an endopeptidases predominantly found in the gastric juice of vertebrates. It hydorlyses only peptide bonds, exhibiting preferential cleavage for hydrophobic amino acids. The optimum pH for the activity of this enzyme is around 1.5, i.e., acidic. Thus, the pI of the enzyme is around this and is equal to 1.0. As the pH increases, there a conformational change in the protein,resulting in the precipitation of the protein.

To be active in an acidic environment, the protein needs the support of acidic amino acids, namely, aspartic acid. This amino acid is protonated for the activity of pepsin.