Which amino acids are most likely involved in holding PLP firmly in the active site when the covalent attachment to alliinase is broken?

• A. Asp and Tyr
• B. Elu and Ser
• C. Arg and Tyr
• D. Lys and Ser

Answer: (C)

The correct answer centers on the specific properties of the amino acids involved in interacting with PLP (pyridoxal phosphate) and maintaining its stability in the active site after covalent attachment has been disrupted.

Arginine and tyrosine are the amino acids that can effectively participate in stabilizing the active site with PLP due to their unique side-chain characteristics. Arginine possesses a positively charged guanidinium group, allowing for strong ionic or electrostatic interactions, as well as potential hydrogen bonding with the negatively charged or polar groups of PLP. This interaction is critical for holding PLP in place due to its significant electronegative character, which is often employed in enzymatic reactions.

Tyrosine, on the other hand, contains a hydroxyl group that can also form hydrogen bonds. This characteristic enables tyrosine to contribute to the binding affinity and stabilization of PLP within the active site. The combination of arginine's ionic interactions and tyrosine's hydrogen bonding potential creates a robust environment for ensuring that PLP remains firmly associated with the enzyme during catalytic processes.

Other options include amino acids that do not provide the same balance of ionic interactions or hydrogen bonding. Therefore, the strong affinity provided by the interactions between arginine