Trypsin, a serine protease that is active in the small intestine (pH ~ 7), is co

Question

Trypsin, a serine protease that is active in the small intestine (pH ~ 7), is concentrated with Asp residues (pKR 3.9) in its active site. It cleaves peptides by binding Lys and Arg residues in the active site. If a mutation occurred where trypsin was expressed in the stomach (pH ~ 2) but remained folded, how would the activity of trypsin change?

a. Trypsin active, change in tertiary structure maintains Asp charge.

b. Trypsin active, metal cofactors maintain some charge on Asp.

c. Trypsin inactive due reduction of disulfide bonds.

d. Trypsin inactive due to protonation of Asp residues under low pH conditions.

e. Trypsin will be more active because if deprotonation of Asp side chains at pH ~2

Explanation / Answer

The Trypsin will be more active because of deprotonation of Asp side chains at ph~2..

In trypsin, the Ser 198 of chymotrypsin, which lies at the bottom of the binding pocket is replaced by Asp. This forms ion pairs with Arg and Lys in the substrate however equally deep slitlike pocket as in chymotrypsin. But the mutation Asp->ser 189 does not convert Trypsin into chymotrypsin.

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