Final answer:
Serine is the amino acid responsible for the nucleophilic attack during the thrombin catalyzed reaction, thanks to its hydroxyl group that acts as a nucleophile.
Step-by-step explanation:
The amino acid that performs the nucleophilic attack during the thrombin catalyzed reaction is serine. This is because serine has a hydroxyl group in its side chain which can act as a nucleophile. During the catalytic mechanism, the hydroxyl group from a serine residue of the enzyme acts as a nucleophile, enabling it to attack the electrophilic carbon atom of the peptide bond. This reaction is a classic example of a nucleophilic acyl substitution mechanism. The ability of serine, threonine, and tyrosine residues to be phosphorylated is due to the hydroxyl group present in their side chains, as this group is capable of acting as a nucleophile and forming a bond with the phosphate group.