Question

Thiol proteases are a widely distributed group ofproteases with a mechanism somewhat similar to that of the serineproteases (the family of enzymes which includes chymotrypsin). Theactive site of one such protease, papain, contains a Cys and oneother amino acid which along with the Cys facilitatescatalysis.

A. To which amino acid in the catalytic triad ofchymotrypsin is the Cys analogous?

B. What do you believe the other amino acid is most likelyto be? Why?

C. What sort of catalysis is the enzyme using the Cys toperform (proximity and orientation, general acid or base,etc.)?