page_title: Oxalyl-CoA decarboxylase
section_title: Reaction mechanism
hierarchical_section_title: Oxalyl-CoA decarboxylase / Reaction mechanism
caption_attribution_description: English: Simplified mechanism of OXC enzyme
context_page_description: In enzymology, an oxalyl-CoA decarboxylase is an enzyme primarily produced by the gastrointestinal bacterium Oxalobacter formigenes that catalyzes the chemical reaction
  oxalyl-CoA formyl-CoA + CO₂
  OXC belongs to the family of lyases, specifically the carboxy-lyases, which cleave carbon-carbon bonds. The systematic name of this enzyme class is oxalyl-CoA carboxy-lyase. Other names in common use include oxalyl coenzyme A decarboxylase, and oxalyl-CoA carboxy-lyase. This enzyme participates in glyoxylate and dicarboxylate metabolism. It employs one cofactor, thiamin diphosphate, and plays a key role in catabolism of oxalate, a highly toxic compound that is a product of the oxidation of carbohydrates in many bacteria and plants. Oxalyl-CoA decarboxylase is extremely important for the elimination of ingested oxalates found in human foodstuffs like coffee, tea, and chocolate, and the ingestion of such foods in the absence of Oxalobacter formigenes in the gut can result in kidney disease or even death as a result of oxalate poisoning.
context_section_description: 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.
caption: Simplified reaction mechanism of oxalyl-CoA decarboxylase. The unlabeled base is believed to be the 4'-imino group of TPP.
exif: {}