"N-Tosylamido-L-phenylethyl, also called tosyl phenylalanyl chloromethyl ketone (TPCK), irreversibly inhibits chymotrypsin, and is used to label the active site histidine residue. The COCH2Cl group is the reactive group that binds to the His residue." 1. Why does chymotrypsin bind TPCK?

a. TPCK is a polar molecule and easily forms several noncovalent interactions with the active site of chyrnotrypsin, reversibly outcompeting the usual substrate.
b. The chlorine of TPCK is a strong nucleophile, and attacks the His 157 residue.
c. The serine residue at position 195 in & pymotrypsin is a strong nucleophile.
d. The phenyl group of TPCK is structurally similar to regular chymotrypsin substrates.

2. Trypsin, another serine protease, does not bind TPCK. How could TPCK be modified to enable its recognition by trypsin?