Identification of the lysine residue modified during the activation of acetimidylation of horse liver alcohol dehydrogenase.

This research study focused on identifying the specific lysine residue that was modified during the activation of acetimidylation of horse liver alcohol dehydrogenase—a protein crucial for breaking down alcohol in the liver. The research determined that lysine residue 228 on the active site of the enzyme was modified with a radioactive acetimidyl group, resulting in an increased enzyme activity.

Methodology

• The researchers used a differential labeling process to modify a single amino group in horse liver alcohol dehydrogenase with methyl(14C)acetimidate.
• The lysine residues not situated in the active site were modified with ethyl acetimidate. Meanwhile, a lysine residue in the active site was protected by creating an enzyme-NAD+-pyrazole complex. This was done to prevent modification of this residue during the initial labelling step.

Results and Analysis

• Once the protecting reagents were removed, the researchers treated the enzyme with methyl(14C)acetimidate. They found that enzyme activity was enhanced 13-fold when 1.1 (14C)acetimidyl group was incorporated into each active site. This indicated that the modification of the specific lysine residue induced a significant increase in enzyme activity.
• Further analysis was conducted to identify the modified lysine residue. A labeled peptide was isolated from a tryptic-chymotryptic digest of the modified enzyme, returning a 35% overall yield.
• The amino acid composition was analysed. Through consecutive Edman degradations, the labeled peptide was identified as residues 219-229, proving that the lysine residue at the 228th position was the one that got modified with the radioactive acetimidyl group.

Conclusion

• The research concluded that the modification of the lysine residue at the 228th position in the active site of the enzyme significantly increases the activity of the horse liver alcohol dehydrogenase. Knowledge of this specific amino acid modification can have implications for understanding the structure-function relationship in enzymes and may also be applied to potential therapeutic approaches for conditions related to liver function.