PURIFICATION AND PROPERTIES OF AN EXTREMELY THERMOSTABLE NADP(-SPECIFIC GLUTAMATE-DEHYDROGENASE FROM ARCHAEOGLOBUS-FULGIDUS())

NADP(+)-specific glutamate dehydrogenase (EC 1.4.1.4) was purified to homogeneity from the extremely thermophilic, strictly anaerobic, sulfa te-reducing archaeon Archaeoglobus fulgidus strain 7324. The native en zyme (263 kDa) is composed of subunits of mol. mass 46 kDa, suggesting a hexameric structure. The temperature optimum for enzyme activity wa s > 95 degrees C. The enzyme was highly thermostable, having a half-li fe of 140 min at 100 degrees C. Potassium phosphate, KCl, and NaCl enh anced the thermal stability and increased the rate of activity three-t o fourfold. The N-terminal 26-amino-acid sequence showed a high degree of similarity to glutamate dehydrogenases from Pyrococcus spp. and Th ermococcus spp.