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A new enzyme which catalyzes the transamination of L-norleucine (2-aminohexanoic acid) and L-leucine with 2-oxoglutarate was purified to homogeneity from cells of Candida guilliermondii var. membranaefaciens. The relative molecular mass determined by gel filtration was estimated to be close to 100 000. The transaminase behaved as a dimer which consists of two subunits identical in molecular mass (Mr 51 000). The enzyme has a maximum activity in the pH range of 8.0-8.5 and at 55°C. 2-Oxoglutarate, and to a lesser extent pyridoxal 5'phosphate, were effective protecting agents against increasing temperature. The enzyme exhibits absorption maximum at 330 nm and 410 nm. L-Norleucine, and L-leucine to a lesser extent, are the best amino donors with 2-oxoglutarate as amino acceptor. The Km values for L-norleucine, L-leucine and 2-oxoglutarate determined from the Lineweaver-Burk plot were 1.8 mM, 6.6 mM and 2.0 mM respectively. A ping-pong bi-bi mechanism of inhibition with alternative substrates is found when the enzyme is in the presence of both L-norleucine and Lleucine. The inhibitory effect of various amino acid analogs on the transamination reaction between L-norleucine and 2-oxoglutarate was studied and Ki values were determined. [ABSTRACT FROM AUTHOR]

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 o)-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 = 35.5 mM and Ki = 33.2 mM respectively). Propionic and butyric acids are also inhibitors (Ki = 3 mM and Ki = 2 mM). [ABSTRACT FROM AUTHOR]