Question

Which of the following reactions needs catalyses by decarboxylase enzyme?
A. Conversion of citric acid to cis-aconitic acid
B. Fumaric acid to malic acid
C. Oxalosuccinic acid to alpha ketoglutaric acid
D. Malic acid to oxaloacetic acid

Answer 1

Hint: Pyruvate decarboxylase is a homotetrameric enzyme which catalyses the decarboxylation of pyruvic acid to acetaldehyde and carbon dioxide in the cytoplasm of prokaryotes and in the cytoplasm and mitochondria of eukaryotes.

Complete step by step answer: Oxalosuccinate is decarboxylated to form $\alpha - Ketoglutarate$ with the help of the enzyme decarboxylase. It is one of the steps involved in the Krebs cycle. It releases one molecule of $C{O_2}$. Oxalosuccinic acid is a substrate of the citric acid cycle. It is acted upon by isocitrate dehydrogenase. Salts and esters of oxalosuccinic acid are known as oxalosuccinate. It is also known as 2-oxo-acid carboxylase, alpha-keto acid carboxylase and pyruvate decarboxylase. In anaerobic conditions, this enzyme is part of the fermentation process that occurs in yeast, especially of the genus Saccharomyces, to produce ethanol by fermentation. t is also present in some species of fish where it permits the fish to perform ethanol fermentation when oxygen is scarce. Pyruvate decarboxylase starts this process by converting the pyruvate into acetaldehyde and carbon dioxide. It depends on cofactors thiamine pyrophosphate (TPP) and magnesium. This enzyme should not be mistaken for the unrelated enzyme pyruvate dehydrogenase, an oxidoreductase, that catalyzes the oxidative decarboxylation of pyruvate to acetyl-CoA.
Hence, the correct answer is option C.

Note: Pyruvate decarboxylase occurs as a dimer of dimers with two active sites shared between the monomers of each dimer. The enzyme contains a beta-alpha-beta structure, yielding parallel beta-sheets. It contains 563 residue subunits in each dimer; the enzyme has strong inter-monomer attractions, but the dimers loosely interact to form a loose tetramer.