Valine dehydrogenase from a non-spore-forming bacterium, Alcaligenes faecalis: purification and characterization

An NAD-dependent valine dehydrogenase (L-valine:NAD oxidoreductase, deaminating, EC 1.4.1.-), was found in a non-spore-forming bacterium, Alcaligenes faecalis, and purified about 80-fold to be characterized. The molecular mass of the enzyme was estimated to be about 72 kDa and the enzyme consists of two identical subunits with a molecular mass of 40 kDa and is thermolabile. It loses its activity fully on incubation at 50 degrees C for 5 min. The enzyme catalyzes the reversible deamination of L-valine, which is the preferred substrate, and other branched-chain and straight-chain L-amino acids in the presence of NAD. The pH optima are about 10.8 and 8.8 for the oxidative deamination and reductive amination, respectively. The pro-S hydrogen at C-4 of the dihydronicotinamide ring of NADH was exclusively transferred to the substrate in the reductive amination. The amino-acid composition markedly differs from those of Bacillus sphaericus and Clostridium thermoaceticum leucine dehydrogenases. The enzyme did not react with the antibody of C. thermoaceticum leucine dehydrogenase. Therefore, the enzyme is clearly different from leucine dehydrogenases from spore-forming bacteria, which act on valine, and the first valine dehydrogenase to be characterized in detail.