Sandbox Reserved 1056: Difference between revisions
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==Mechanism== | ==Mechanism== | ||
[[Image:Real_Mechanism.png|400 px|right|thumb|Figure 6: Chemical Mechanism of Isocitrate Lyase. Note: The mechanism depicted in this image is the reverse process, but the mechanism is identical.]] | [[Image:Real_Mechanism.png|400 px|right|thumb|Figure 6: Chemical Mechanism of Isocitrate Lyase. Note: The mechanism depicted in this image is the reverse process, but the mechanism is identical.]] | ||
Isocitrate lyase catalyzes a reversible aldol condensation, converting isocitrate to glyoxylate and succinate via the breaking of a C-C bond.<ref name="claisen"/> Within the active site of ICL the HIS193 residue deprotonates the <scene name='69/694223/Arginine/3'>Cys191</scene>residue of the active site in order to increase its basicity.<ref name="ICL">PMID:10932251</ref><ref name="claisen"/> The Cys 191 residue then deprotonates the alpha carbon adjacent to one of the carbonyl groups of succinate, thus forming the enolic intermediate.<ref name="claisen"/> The negatively charged alpha carbon atom of the enolic intermediate acts as a nucleophile that attacks the carbonyl carbon of the aldehyde of glyoxylate. The nucleophilic attack will place a negative charge on the oxygen atom oxygen at the former carbonyl oxygen of the aldehyde, which will be stabilized by positive charges of the Mg ion, ARG228 and HIS180.<ref name="ICL">PMID:10932251</ref> The protonation of this species will yield the final product. It is important to note that this reaction is entirely reversible; the breakdown of isocitrate into glyoxylate and succinate occurs using a similar mechanism. | Isocitrate lyase catalyzes a reversible aldol condensation, converting isocitrate to glyoxylate and succinate via the breaking of a C-C bond.<ref name="claisen"/> Within the active site of ICL the HIS193 residue deprotonates the <scene name='69/694223/Arginine/3'>Cys191</scene> residue of the active site in order to increase its basicity.<ref name="ICL">PMID:10932251</ref><ref name="claisen"/> The Cys 191 residue then deprotonates the alpha carbon adjacent to one of the carbonyl groups of succinate, thus forming the enolic intermediate.<ref name="claisen"/> The negatively charged alpha carbon atom of the enolic intermediate acts as a nucleophile that attacks the carbonyl carbon of the aldehyde of glyoxylate. The nucleophilic attack will place a negative charge on the oxygen atom oxygen at the former carbonyl oxygen of the aldehyde, which will be stabilized by positive charges of the Mg ion, ARG228 and HIS180.<ref name="ICL">PMID:10932251</ref> The protonation of this species will yield the final product. It is important to note that this reaction is entirely reversible; the breakdown of isocitrate into glyoxylate and succinate occurs using a similar mechanism. | ||