Sandbox Reserved 1056: Difference between revisions

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 CYS191 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.