A second NAD-dependent valine dehydrogenase (VDH) of was detected and purified to homogeneity by affinity chromatography on Reactive-Blue 2 Sepharose followed by gel filtration and Mono Q fast protein liquid chromatography. The relative molecular masses of the native enzyme and its subunits were determined to be 80000 and 41000, respectively, indicating that the enzyme is a homodimer. The enzyme was the only active VDH in ; its activity was significantly induced by L-valine, but was repressed by ammonia. Among branched- and straight-chain amino acids that serve as enzyme substrates, L-2-aminobutyrate and L-valine are preferred. Significant activities were found with deamino-NAD and 3-pyridinealdehyde-NAD. The molecular and catalytic properties of the enzyme distinguish it from the enzyme previously purified, and thus indirectly indicate the existence of two VDH in


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