Page 179 - The Manga Guide to Biochemistry

For example, one of the protein catabolism enzymes secreted from the pancreas,
carboxypeptidase, detaches amino acids sequentially from the end of a protein.

Carboxypeptidase comes in various types, including A, B, C, and Y. Carboxypepti-
dase A, for example, can detach almost any amino acid from the C-terminal end of a
protein, but it doesn’t work well on amino acids with bulky or aromatic R-groups, like
arginine, lysine, and proline.

Proline Arginine Lysine

N-terminal C-terminal C-terminal C-terminal
side of side of
Arginine lysine Relaaaaxed
Carboxy-
C-terminal I’ll detach peptidase A
side of anything other
proline than arginine,

lysine, or
proline.

There are 20 types of amino acids that make up proteins, right? So even though
carboxypeptidase A can’t deal with arginine, lysine, and proline, there are still 17
types it can deal with. It seems pretty flexible!

That’s right. It has some serious leeway in the substrates it can interact with.
However, there are also some “strict” protein catabolism enzymes. For example,

trypsin cuts only through the C-terminal side of arginine and lysine.

Arginine Lysine

C-terminal side C-terminal side Strict!
of Arginine of lysine Trypsin

Enzymes Are the Keys to Chemical Reactions 165