Degradation of Pyrimidines in Saccharomyces Kluyveri: Transamination of β-Alanine

Abstract

Beta-alanine is an intermediate in the reductive degradation of uracil. Recently we have identified and characterized the Saccharomyces kluyveri PYD4 gene and the corresponding enzyme β -alanine aminotransferase ( ^Sk Pyd4p), highly homologous to eukaryotic γ-aminobutyrate aminotransferase (GABA-AT). S. kluyveri has two aminotransferases, GABA aminotransferase ( ^Sk Uga1p) with 80% and ^Sk Pyd4p with 55% identity to S. cerevisiae GABA-AT. ^Sk Pyd4p is a typical pyridoxal phosphate-dependent aminotransferase, specific for α -ketoglutarate (α KG), β -alanine (BAL) and γ -aminobutyrate (GABA), showing a ping-pong kinetic mechanism involving two half-reactions and substrate inhibition. ^Sk Uga1p accepts only α KG and GABA but not BAL, thus only ^Sk Pydy4p belongs to the uracil degradative pathway.

Keywords:

• Aminotransferase
• β-alanine
• γ-aminobutyrate
• gene duplication
• Saccharomyces kluyveri