4-Aminobutyrate: 2-oxoglutarate aminotransferase from Candida. Purification and properties

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Abstract
An enzyme which catalyzes the transamination of 4-aminobutyrate with 2-oxoglutarate was Purified 588-fold to homogeneity from Candida guilliermondii var. membranaefaciens, grown with 4-aminobutyrate as sole source of nitrogen. An apparent relative molecular mass of 107000 was estimated by gel filtration. The enzyme was found to be a dimer made up of two subunits identical in molecular mass (Mr 55000). The enzyme has a maximum activity in the pH range 7.8–8.0 and a temperature optimum of 45°C. 2-Oxoglutarate protects the enzyme from heat inactivation better than pyridoxal 5′-phosphate. The absorption spectrum of the enzyme exhibits two maxima at 412 nm and 330 nm. The purified enzyme catalyzes the transamination of ω-amino acids; 4-aminobutyrate is the best amino donor and low activity is observed with β-alanine. The Michaelis constants are 1.5 mM for 2-oxoglutarate and 2.3 mM for 4-aminobutyrate. Several amino acids, such as α,β-alanine and 2-aminobutyrate, are inhibitors (Ki= 38.7 mM, Ki= 35.5mM and Ki= 33.2 mM respectively). Propionic and butyric acids are also inhibitors (Ki= 3 mM and Ki= 2 mM).