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. Thefore, 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.