GLUTAMATE-DEHYDROGENASE FROM THE EXTREMELY THERMOPHILIC ARCHAEBACTERIAL ISOLATE AN1

Glutamate dehydrogenase (L-glutamate:NADP+ oxidoreductase, deaminating and transaminating, EC 1.4.1.4) was purified to homogeneity from the extremely thermophilic archaebacterial isolate AN1 (a member of the Thermococcales). The enzyme comprised a large proportion of the soluble cell protein (11%) and was purified in high yield. The molecular mass of the native enzyme was 204 kDa, while the subunit molecular mass was 47 kDa, indicating a tetrameric structure. The enzyme is specific for NADP(H) rather than NAD(H) by a factor of greater than 1000, as judged by V(max)/K(m). Glutamate synthase activity was about 50% of the glutamate dehydrogenase activity. Activity was markedly enhanced by calcium, magnesium and manganese ions. The enzyme was highly thermostable with t1/2 values of 12.5 h and 47 min at 90-degrees-C and 103-degrees-C, respectively.