Purification of NADP-dependent glutamate dehydrogenase from Pseudomonas aeruginosa and immunochemical characterization of its in vivo inactivation

Carbon source-dependent modulation of NADP-glutamate dehydrogenases in isophthalate-degrading Pseudomonas aeruginosa strain PP4, Pseudomonas strain PPD and Acinetobacter lwoffii strain ISP4

Acinetobacter lwoffii strain ISP4 metabolizes isophthalate rapidly compared with Pseudomonas aeruginosa strain PP4 and Pseudomonas strain PPD. Isophthalate has been reported to be a potent competitive inhibitor of glutamate dehydrogenase (GDH). Exogenous supplementation of isophthalate with glutamate or alpha-ketoglutarate at 1 mM concentration caused strains PP4 and PPD to grow faster than in the presence of isophthalate alone; however, no such effect was observed in strain ISP4. When grown on isophthalate, all strains showed activity of NADP-dependent GDH (NADP-GDH), while cells grown on glucose, 2x yeast extract-tryptone broth (2YT) or glutamate showed activities of both NAD-dependent GDH (NAD-GDH) and NADP-GDH. Activity staining, inhibition and thermal stability studies indicated the carbon source-dependent presence of two (GDH(I) and GDH(II)), three (GDH(A), GDH(B) and GDH(C)) and one (GDH(P)) forms of NADP-GDH in strains PP4, PPD and ISP4, respectively. The results demonstrate the carbon source-dependent modulation of different forms of NADP-GDH in these bacterial strains. This modulation may help the efficient utilization of isophthalate as a carbon source by overcoming the inhibitory effect on GDH.

Purification and characterization of the NADP-dependent glutamate dehydrogenase from Bacillus fastidiosus

Ammonia assimilation in Bacillus fastidiosus proceeds via the NADP-dependent glutamate dehydrogenase. The enzyme, purified to homogeneity, is composed of identical subunits with a molecular weight of about 48,000 dalton. Presumably the enzyme is a hexamer. The enzyme is specific for NADP(H). The pH optima for the amination and deamination reactions are 7.7 and 8.6, respectively. The temperature optimum is 60 degrees C. Furthermore, temperature stability and apparent Km values for substrates of both the amination and deamination reactions were determined. Several metabolites were tested for their effect on the enzyme activity. Only malate and fumarate showed some inhibitory effect.

Induction, isolation, and some properties of the NADPH-dependent glutamate dehydrogenase from the nonheterocystous cyanobacterium Phormidium laminosum

The level of the NADPH-dependent glutamate dehydrogenase activity (EC 1.4.1.4) from nitrate-grown cells of the thermophilic non-N2-fixing cyanobacterium Phormidium laminosum OH-1-p.Cl1 could be significantly enhanced by the presence of ammonium or nitrite, as well as by L-methionine-DL-sulfoximine and other sources of organic nitrogen (L-Glu, L-Gln, and methylamine). The enzyme was purified more than 4,400-fold by ultracentrifugation, ion-exchange chromatography, and affinity chromatography, and at 30 degrees C it showed a specific activity of 32.9 mumol of NADPH oxidized per min per mg of protein. The purified enzyme showed no aminotransferase activity and catalyzed the amination of 2-oxoglutarate preferentially to the reverse catabolic reaction. The enzyme was very specific for its substrates 2-oxoglutarate (Km = 1.25 mM) and NADPH (Km = 64 microM), for which hyperbolic kinetics were obtained. However, negative cooperativity (Hill coefficient h = 0.89) and [S]0.5 of 18.2 mM were observed for ammonium. The mechanism of the aminating reaction was of a random type with independent sites. The purified enzyme showed its maximal activity at 60 degrees C (Ea = 5.1 kcal/mol [21.3 kJ/mol]) and optimal pH values of 8.0 and 7.5 when assayed in Tris hydrochloride and potassium phosphate buffers, respectively. The native molecular mass of the enzyme was about 280 kilodaltons. The possible physiological role of the enzyme in ammonia assimilation is discussed.