Comparison of two glutamate producing enzymes from the hyperthermophilic archaeon Pyrococcussp. KOD1

The glutamate dehydrogenase from Pyrococcussp. KOD1 (Pk‐GDH) was purified to homogeneity and its enzymatic characteristics for glutamate production were analyzed. Pk‐GDH exhibited glutamate producing activity from glutamine, which was found in some higher eukaryotic GDHs. However, the kcat/Kmvalues for ammonia and glutamine were 15×103min−1mM and 0.4×103min−1mM, respectively, indicating that the enzyme utilizes ammonia predominantly for glutamate production. Kinetic parameters of Pk‐GDH were compared with those of Pk‐GltA, which was previously identified as a glutamate synthase homologue. The turnover number for glutamine of Pk‐GltA (4.1×103min−1mM) was 10‐fold higher than that of Pk‐GDH (0.4×103min−1mM). Therefore, Pk‐GDH is less efficient than Pk‐GltA for glutamate production. Pk‐GDH utilized both NADPH and NADH as a cofactor, Pk‐GltA utilized only NADPH.