NAD-DEPENDENT GLUTAMATE-DEHYDROGENASE FROM THE THERMOPHILIC EUBACTERIUM BACILLUS-ACIDOCALDARIUS

The first thermophilic eubacterial glutamate dehydrogenase was purified to homogeneity from Bacillus acidocaldarius to compare its molecular properties with those of the glutamate dehydrogenase from thermophilic archaea. Glutamate dehydrogenase represents 2% of the total soluble proteins of B. acidocaldarius, an amount that may suggest an important role for this enzyme in nitrogen metabolism of the thermophilic eubacterium. The protein is a hexamer (subunit mass 48 kDa) and undergoes dissociation during gel filtration analysis. Isoelectric focusing of the purified enzyme indicated a pI of 4.5. The enzyme is strictly specific for NAD, 2-oxoglutarate, and L-glutamate. The thermal stability of B. acidocaldarius glutamate dehydrogenase is dependent on protein concentration.