The enzyme papain is a thiol protease, using a mechanism similar to the mechanis

Question

The enzyme papain is a thiol protease, using a mechanism similar to the mechanism used by chymotrypsin, except that there is an active site Cys in papain carrying out the catalytic role played by the active site Ser of chymotrypsin. There is a His residue in papain that plays the same role as the active site His residue in chymotrypsin.

1) Name the region of the chymotrypsin active site responsible for tight transition state binding in chymotrypsin’s chemical mechanism.

2) Like chymotrypsin, papain should also have a region responsible for binding/stabilizing the transition state in its peptide hydrolysis mechanism. Use your knowledge of the mechanism of chymotrypsin to name the structural element of the transition state that would be tightly bound by papain. (You don’t need to draw a structure.)

Explanation / Answer

1. Oxyanion hole 2. The structural element of the transition site that would bind to the oxyanion hole is a carbon surrounded by 3 electronegative atoms with one of them having a negative charge.

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