Fructose Bisphosphate Aldolase: Difference between revisions

The reaction is an aldol cleavage, or otherwise termed, retro aldo condensation.  Catalysis occurs first when the nucleophilic ε-amine group of Lys229 attacks the carbonyl (alpha) carbon of the substrate (FBP) in its open-ring state, pushing an electron pair to the oxygen of the carbonyl.  The oxygen is protonated and leaves as water as a protonated <scene name='Austin_Drake_Sandbox/Schiff_base/2'>Schiff base</scene> is produced (an imine resulting from a ketone and amine) with the open-ring form of FBP, accompanied by electrostatic stabilization from <scene name='Austin_Drake_Sandbox/Catalytic_site_w_water/5'>Asp33</scene>.  Aldol cleavage between C3 and C4 produces GAP and an enamine precursor to DHAP.<ref name="book" />  The cleavage is facilitated by the positive charge from the Schiff base.  The subsequent electron movement, which alleviates the positive charge, also breaks the C3-C4 bond.<ref name="review" />  Tautomerization, protonation and the hydrolysis of the Schiff base produce the final product of DHAP and regenerate the enzyme.  The catalysis is driven by the more favorable stability of the protonated Schiff base compared to the enolate that would appear in basic catalysis pathways.<ref name="book" />   

'''Kinetics'''