Pyruvate synthase


In enzymology, a pyruvate synthase is an enzyme that catalyzes the interconversion of pyruvate and acetyl-CoA. It is also called pyruvate:ferredoxin oxidoreductase.
The relevant equilibrium catalysed by PFOR is:
The 3 substrates of this enzyme are pyruvate, CoA, and oxidized ferredoxin, whereas its 3 products are acetyl-CoA, CO2, and reduced ferredoxin.

Function

This enzyme participates in 4 metabolic pathways: pyruvate metabolism, propanoate metabolism, butanoate metabolism, and reductive carboxylate cycle.
Its major role is the extraction of reducing equivalents by the decarboxylation. In aerobic organisms, this conversion is catalysed by pyruvate dehydrogenase, also uses thiamine pyrophosphate but relies on lipoate as the electron acceptor. Unlike the aerobic enzyme complex PFOR transfers reducing equivalents to flavins or iron-sulflur clusters. This process links glycolysis to the Wood–Ljungdahl pathway.

Nomenclature

This enzyme belongs to the family of oxidoreductases, specifically those acting on the aldehyde or oxo group of donor with an iron-sulfur protein as acceptor. The systematic name of this enzyme class is pyruvate:ferredoxin 2-oxidoreductase . Other names in common use include:
PFOR adopts a dimeric structure, while each monomeric subunit is composed of one or multiple chain of polypeptides. Each monomeric subunit of PFOR consists of six domains binding one TPP molecule and three clusters.

Catalytic Mechanism

An PFOR reaction starts with the nucleophilic attack of C2 of TPP on the 2-oxo carbon of pyruvate, which forms a lactyl-TPP adduct. Next, the lactyl-TPP adduct releases the CO2 moiety, forming an anionic intermediate, which then transfer an electron to a cluster. These steps lead to a stable radical intermediate that can be observed by electron paramagnetic resonance experiments. The radical intermediate reacts with a CoA molecule, transfers another electron from the radical intermediate to a cluster and forms an acetyl-CoA product.

Inhibitors