Reaction Mechanism
A key feature of the cofactor TPP is the relatively acidic proton bound to the carbon atom between the nitrogen and sulfur in the thiazole ring, which has a pKa near 10. This carbon center ionizes to form a carbanion, which adds to the carbonyl group of oxalyl-CoA. This addition is followed by the decarboxylation of oxalyl-CoA, and then the oxidation and removal of formyl-CoA to regenerate the carbanion form of TPP. While the reaction mechanism is shared with other TPP-dependent enzymes, the residues found in the active site of OXC are unique, which has raised questions about whether TDP must be deprotonated by a basic amino acid at a second site away from the carbanion-forming site to activate the cofactor.
Read more about this topic: Oxalyl-Co A Decarboxylase
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