Isoelectric Point of Pepsin Pepsin is the name given to several digestive enzyme

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?

Explanation / Answer

Pepsin shows maximum activity ( about 90 percent) at pH 1.5. Thus the isoelectric point should be less than 1.5. Pepsin shows isoelectric point at around pH 1.0.

For such an isoelectric point pepsin should have acidic amino acids in abundant. Functional groups like carboxylic acid, alcohol group, thiol etc would confer acidic character.

Amino acids like Aspartic Acid, Glutamic acid would contribute to such groups.

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