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Appl Microbiol Biotechnol. 2004 Sep;65(4):414-8. Epub 2004 May 4.

Inactivation of pycA, encoding pyruvate carboxylase activity, increases poly-beta-hydroxybutyrate accumulation in Azotobacter vinelandii on solid medium.

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Departamento de Microbiología Molecular, Instituto de Biotecnología, Universidad Nacional Autónoma de México, Apartado Postal 510-3, 62250, Cuernavaca, Morelos, Mexico.


Strain AJ1678, an Azotobacter vinelandii mutant overproducing the storage polymer poly-beta-hydroxybutyrate (PHB) in solid but not liquid complex medium with sucrose, was isolated after mini-Tn5 mutagenesis of strain UW136. Cloning and nucleotide sequencing of the affected locus led to identification of pycA, encoding a protein with high identity to the biotin carboxylase subunit of pyruvate carboxylase enzyme (PYC). A gene ( pycB) whose product is similar to the biotin-carrying subunit of PYC is present immediately downstream from pycA. An assay of pyruvate carboxylase activity and an avidin-blot analysis confirmed that pycA and pycB encode the two subunits of this enzyme. In many organisms, PYC catalyzes ATP-dependent carboxylation of pyruvate to generate oxaloacetate and is responsible for replenishing oxaloacetate for continued operation of the tricarboxylic acid cycle. We propose that the pycA mutation causes a slow-down in the TCA cycle activity due to a low oxaloacetate concentration, resulting in a higher availability of acetyl-CoA for the synthesis of poly-beta-hydroxybutyrate.

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