Question

Isoelectric Point of Pepsin Pepsin is the name given to several digestive enzymes secreted (as larger precursor proteins) by glands that line the stomach. These glands also secrete hydrochloric acid, which dissolves the particulate matter in food, allowing pepsin to enzymatically cleave individual protein molecules. The resulting mixture of food, HCl, 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 this pI on pepsin? Which amino acids in the proteins would contribute such groups?

Answer 1

Pepsin proteins are acidic in nature and have relatively low PI(they have PH near to digestive juices).They always be active in PH of stomach.Actually pepsin is the mixture of enzymes which have pI nearby to 1.Pepsin is active only in stomach because stomach only have PH which would be suitable for pepsin to perform its work better,in the higher PH of intestine pepsin become inactive and be unable to perform its function.

  Pepsin have low pI so it require large number of negatively charged groups and these negatively charged groups contributed by carboxylate group of aspartic acid and glutamic acid residues.