Reactivity of intermediates in benzoylformate decarboxylase: avoiding the path to destruction.
Benzoylformate decarboxylase forms a covalent intermediate from thiamin diphosphate (TDP) and benzoylformate, alpha-mandelylTDP. This loses carbon dioxide to form a carbanion (enamine). Protonation of the carbanion and elimination of benzaldehyde regenerate enzyme-bound TDP. We synthesized alpha-mandelylthiamin and found that the rate of the loss of carbon dioxide is one-millionth that of the enzymic reaction. Thus, the enzyme provides an environment that facilitates the unimolecular decarboxylation process. However, the resulting nonenzymic carbanion reacts very rapidly to give products that lead to the irreversible destruction of the cofactor. This contrasts with the normal process on the enzyme. Brønsted acids on the enzyme may divert the reaction to the benzaldehyde precursor, or the enzyme may block access to the pathway that leads to destruction of the cofactor.
Hu
Qingyan
Q
Davenport Chemical Laboratory, Department of Chemistry, University of Toronto, Toronto, Ontario, Canada M5S 3H6.
Kluger
Ronald
R
D002262:Carboxy-Lyases / Q000737:chemistry* / Q000378:metabolism; D003653:Decarboxylation; D006038:Glyoxylates / Q000737:chemistry / Q000378:metabolism; D007700:Kinetics; D008333:Mandelic Acids / Q000138:chemical synthesis / Q000737:chemistry; D013831:Thiamine / Q000031:analogs & derivatives / Q000138:chemical synthesis / Q000737:chemistry
D006038:Glyoxylates; D008333:Mandelic Acids; C471686:alpha-mandelylthiamin; C012482:phenylglyoxylic acid; D002262:Carboxy-Lyases; C019778:benzoylformate decarboxylase; D013831:Thiamine