2-Hydroxyacid dehydrogenase from Haloferax mediterranei, a D-isomer-specific member of the 2-hydroxyacid dehydrogenase family

An NAD-dependent D-2-hydroxyacid dehydrogenase (EC 1.1.1.) was isolated and characterized from the halophilic Archaeon Haloferax mediterranei. The enz yme is a dimer with a molecular mass of 101.4 +/- 3.3 kDa. It is strictly N AD-dependent and exhibits its highest activity in 4 M NaCl. The enzyme is c haracterized by a broad substrate specificity 2-ketoisocaproate and 2-ketob utyrate being the substrates with the higher V-max/K-m. When pyruvate and 2 -ketobutyrate were the substrates the optimal pH was acidic (pH 5) meanwhil e for 2-ketoisocaproate maximum activity was achieved at basic pH between 7 .5 and 8.5. The optimum temperature was 52 degreesC and at 65 degreesC ther e was a pronounced activity decrease. This new enzyme can be used for the p roduction of D-2-hydroxycarboxylic acid. (C) 2000 Societe francaise de bioc himie et biologie moleculaire / Editions scientifiques et medicales Elsevie r SAS.