Thiol proteases are a widely distributed group of proteases with a mechanism somewhat similar to that of the serine proteases (the family of enzymes which includes chymotrypsin). The active site of one such protease, papain, contains a Cys and one other amino acid which along with the Cys facilitates catalysis.
A. To which amino acid in the catalytic triad of chymotrypsin is the Cys analogous?
B. What do you believe the other amino acid is most likely to be? Why?
C. What sort of catalysis is the enzyme using the Cys to perform (proximity and orientation, general acid or base, etc.)?
