Page - (000044) - in Biomedical Chemistry: Current Trends and Developments

Scheme 1.1.29: Mechanism of an aldol addition in a class I fructose-biphosphate aldolase. Class I fructose-biphosphate aldolases have another stabilization mechanism that does not resemble a regular aldol reaction, though the final product is the same (Scheme 1.1.30). The mechanism occurs in the following abbreviated steps: 1. A carbinolamine is formed by nucleophilic addition of a lysine residue to DHAP 2. The carbinolamine eliminates water through acid/base catalysis, forming an enamine 3. The enamine acts as an enol (through analogous resonance structures) and adds to GAP 4. Water is added to the resulting iminium ion (hydrolysis is the reverse of the imine synthesis) 5. The carbonyl and lysine residue are regenerated from the new carbinolamine.