Enzyme Mechanisms - Serine Proteases
Part III
Part III. Target Amino Acids of Serine Proteases.
All three enzymes hydrolyze the same bond in peptides (ie the peptide bond) but they have different target AAs.
Trypsin - Arg Lys
Chymotrypsin - Phe Tyr Trp
Elastase - Ala Ser Val Thr
To accommodate these different substrates, the substrate binding pocket is adjusted in each enzyme as shown below.
Figure 9. Substrate binding pockets for A) Trypsin; B) Chymotrypsin; and C) Elastase. The positively charged Lys and Arg of the target amino acid fits into a deep pocket with a negatively charged amino acid (Asp-189) at its base. The aromatic amino acid side chains of Phe, Tyr and Trp fit into a hydrophobic pocket of chymotrypsin, while the small side chains of amino acids like Ala fit into substrate pocket of elastase, which would exclude large and bulky side chains.
Figure probably from an old Lenhinger Biochemistry who owns the copyright.
©Wilbur H. Campbell, 1995; wcampbel@mtu.edu