Novel halophilic 2-aminobutyrate dehydrogenase from Halobacterium saccahrovorum DSM 1137

Abstract

A halophilic NAD +-dependent 2-aminobutyrate dehydrogenase (EC1.4.1.1) was purified to homogeneity from a crude extract of an extreme halophile, Halobacterium saccharovorum DSM 1137, with a 30% yield. The enzyme had a molecular mass of about 160 kDa and consisted of four identical subunits. It retained more than 70% of the activity after heating at 60 °C for 1 h and kept it at 30 °C for 8 months in the presence of 2 M NaCl. The enzyme showed maximum activity in the presence of 2 M RbCl or KCl. The enzyme required NAD + as a coenzyme and used l-2-aminobutyrate, l-alanine, and l-norvaline as substrates. The best substrate was l-2-aminobutyrate. The optimum pH was 9.3 for the oxidative deamination of l-2-aminobutyrate and 8.6 for the reductive amination of 2-ketobutyrate. The Michaelis constants were 1.2 mM for l-2-aminobutyrate, 0.16 mM for NAD +, 0.012 mM for NADH, 0.78 mM for 2-ketobutyrate, and 500 mM for ammonia in the presence of 2 M KCl. The K m values for the substrates depended on the concentration of KCl, and the K m values decreased under high salt conditions.