Valine dehydrogenase (VDH) was purified to homogeneity from cell-free extract of , which produces tylosin. The enzyme was purified 1508-fold in a 17.7% yield using a combination of hydrophobic chromatography and ion-exchange fast protein liquid chromatography. The of the native enzyme was determined to be 218000 and 215000, by equilibrium ultracentrifugation and size-exclusion high-performance liquid chromatography, respectively. The enzyme is composed of 12 subunits of 18000. Using analytical isoelectric focusing the isoelectric point of VDH was found to be 4.7. Oxidative deamination of -valine was optimal at pH 10.6. Reductive amination of 2-oxoisovalerate was optimal at pH 8.8. The Michaelis constants ( ) were 1 m for -valine and 0.029 m for NAD. values for reductive amination were 0.80 m for 2-oxoisovalerate, 0.050 m for NADH and 22 m for NH .


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