Fructose Bisphosphate Aldolase: Difference between revisions
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As an enzyme, the aldolase must not only encourage and favor the hydrolysis of fructose 1,6-bisphosphate, but also bind the substrate so as to hold it in the active site. The main-chain nitrogens of Ser271 and Gly272 hold the 1-phosphate group while the Lys41, Arg42 and Arg303 residues hold the 6-phosphate group. The five proposed binding residues are in close proximity to the catalytic Lys229, implicating them as participants in the binding process.<ref>PMID:10048322</ref> The <scene name='Austin_Drake_Sandbox/Tyr363/1'>C-terminus</scene>, which sits just outside of the barrel and catalytic site, of the enzyme also appears to contribute to the catalytic process of the aldolase. Mutations of suppression of the final tyrosine residue (Tyr363) causes a notable drop in the activity of the enzyme. Two cysteine residues have also been implicated in the catalytic process. Though they do not appear to be necessary for catalysis, modification of them does result in a decrease in catalytic activity. The two Cis residues are far from the active site, but do impact the movement of the C-terminus of the enzyme, which further implicates the terminus as participatory in the catalysis. | As an enzyme, the aldolase must not only encourage and favor the hydrolysis of fructose 1,6-bisphosphate, but also bind the substrate so as to hold it in the active site. The main-chain nitrogens of Ser271 and Gly272 hold the 1-phosphate group while the Lys41, Arg42 and Arg303 residues hold the 6-phosphate group. The five proposed binding residues are in close proximity to the catalytic Lys229, implicating them as participants in the binding process.<ref>PMID:10048322</ref> The <scene name='Austin_Drake_Sandbox/Tyr363/1'>C-terminus</scene>, which sits just outside of the barrel and catalytic site, of the enzyme also appears to contribute to the catalytic process of the aldolase. Mutations of suppression of the final tyrosine residue (Tyr363) causes a notable drop in the activity of the enzyme. Two cysteine residues have also been implicated in the catalytic process. Though they do not appear to be necessary for catalysis, modification of them does result in a decrease in catalytic activity. The two Cis residues are far from the active site, but do impact the movement of the C-terminus of the enzyme, which further implicates the terminus as participatory in the catalysis. | ||
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 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" /> | 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''' | '''Kinetics''' | ||