Molecular interactions of six aromatic competitive inhibitors with bovine liver glutamate dehydrogenase

2008

Indian J Microbiol

Phthalate isomers and their esters are used heavily in various industries. Excess use and leaching from the product pose them as major pollutants. These chemicals are toxic, teratogenic, mutagenic and carcinogenic in nature. Various aspects like toxicity, diversity in the aerobic bacterial degradation, enzymes and genetic organization of the metabolic pathways from various bacterial strains are reviewed here. Degradation of these esters proceeds by the action of esterases to form phthalate isomers, which are converted to dihydroxylated intermediates by specifi c and inducible phthalate isomer dioxygenases. Metabolic pathways of phthalate isomers converge at 3,4-dihydroxybenzoic acid, which undergoes either ortho-or meta-ring cleavage and subsequently metabolized to the central carbon pathway intermediates. The genes involved in the degradation are arranged in operons present either on plasmid or chromosome or both, and induced by specifi c phthalate isomer. Understanding metabolic pathways, diversity and their genetic regulation may help in constructing bacterial strains through genetic engineering approach for effective bioremediation and environmental clean up.

Section: Phthalate Toxicitymentioning

confidence: 99%

Bacterial degradation of phthalate isomers and their esters

2008

Indian J Microbiol

“…Interestingly, GDHs from strains PP4 and ISP4 showed a mixed partial type of inhibition with isophthalate, suggesting that isophthalate binds not only to the enzyme form but also to the enzyme-substrate form. The inhibition constants (K i ) with isophthalate suggested that deamination reactions were far more sensitive to inhibition than amination reactions, as observed with several GDHs (5,13,16,27,28,30,34). The K i values suggested that compared to GDH I , GDH II has a higher affinity for isophthalate, thus making it more susceptible to inhibition.…”

Section: Discussionmentioning

confidence: 91%

“…Compared to the organisms whose metabolic pathways for isophthalate degradation have been studied, a large number of organisms have been studied in detail to determine their metabolic pathways for phthalate and terephthalate degradation (12,17,18,20,25,26,29,31,32,35,36). The fewer isophthalate-degrading strains and the difficulties in isolating them could be due to the fact that isophthalate acts as a competitive inhibitor of glutamate dehydrogenase (GDH), which plays an important role at the interface of C metabolism and N metabolism (5,11,13,16,27,28,30,33,34). GDH performs oxidative deamination of glutamate to ␣-ketoglutarate (␣-KG) and reductive amination of ␣-KG to glutamate, and depending on the cofactor requirement the enzyme is either NAD-, NADP-, or NAD(P)-GDH (7,19).…”

mentioning

confidence: 99%

Bypassing Isophthalate Inhibition by Modulating Glutamate Dehydrogenase (GDH): Purification and Kinetic Characterization of NADP-GDHs from Isophthalate-Degrading Pseudomonas aeruginosa Strain PP4 and Acinetobacter lwoffii Strain ISP4

2010

J Bacteriol

Pseudomonas aeruginosa strain PP4 and Acinetobacter lwoffii strain ISP4 metabolize isophthalate as a sole source of carbon and energy. Isophthalate is known to be a competitive inhibitor of glutamate dehydrogenase (GDH), which is involved in C and N metabolism. Strain PP4 showed carbon source-dependent modulation of NADP-GDH; GDH I was produced when cells were grown on isophthalate, while GDH II was produced when cells were grown on glucose. Strain ISP4 produced a single form of NADP-GDH, GDH P , when it was grown on either isophthalate or rich medium (2YT). All of the forms of GDH were purified to homogeneity and characterized. GDH I and GDH II were found to be homotetramers, while GDH P was found to be a homohexamer. GDH II was more sensitive to inhibition by isophthalate (2.5-and 5.5-fold more sensitive for amination and deamination reactions, respectively) than GDH I . Differences in the N-terminal sequences and electrophoretic mobilities in an activity-staining gel confirmed the presence of two forms of GDH, GDH I and GDH II , in strain PP4. In strain ISP4, irrespective of the carbon source, the GDH P produced showed similar levels of inhibition with isophthalate. However, the specific activity of GDH P from isophthalate-grown cells was 2.5-to 3-fold higher than that of GDH P from 2YT-grown cells. Identical N-terminal sequences and electrophoretic mobilities in the activity-staining gel suggested the presence of a single form of GDH P in strain ISP4. These results demonstrate the ability of organisms to modulate GDH either by producing an entirely different form or by increasing the level of the enzyme, thus enabling strains to utilize isophthalate more efficiently as a sole source of carbon and energy.Phthalate isomers and their esters are used widely in various industries and are considered potent pollutants because of their carcinogenic, mutagenic, teratogenic, and endocrine-disrupting properties (31, 32). Due to the persistence of these compounds in the environment, microorganisms have evolved and adapted to utilize them as sole sources of carbon and energy. Compared to the organisms whose metabolic pathways for isophthalate degradation have been studied, a large number of organisms have been studied in detail to determine their metabolic pathways for phthalate and terephthalate degradation (12,17,18,20,25,26,29,31,32,35,36). The fewer isophthalate-degrading strains and the difficulties in isolating them could be due to the fact that isophthalate acts as a competitive inhibitor of glutamate dehydrogenase (GDH), which plays an important role at the interface of C metabolism and N metabolism (5,11,13,16,27,28,30,33,34). GDH performs oxidative deamination of glutamate to ␣-ketoglutarate (␣-KG) and reductive amination of ␣-KG to glutamate, and depending on the cofactor requirement the enzyme is either NAD-, NADP-, or NAD(P)-GDH (7, 19).Pseudomonas aeruginosa strain PP4 and Acinetobacter lwoffii strain ISP4 utilize isophthalate as a sole source of carbon and energy (31, 32). Thus, in these strains, the carbo...

“…The difficulties in the successful isolation of isophthalatedegrading strains from the environment could be due to the fact that isophthalate acts as a potent competitive inhibitor of GDH, which interlinks carbon and nitrogen metabolism (Boots et al, 1976;Caughey et al, 1957;Cunliffe et al, 1983;Rogers et al, 1972;Stevens et al, 1989). The present study demonstrates that although GDH is inhibited by isophthalate, strains PP4, PPD and ISP4 have adopted different strategies, such as carbon sourcedependent modulation of forms of NADP-GDH, for the effective utilization of isophthalate, and that they thrive in the environment.…”

Section: Carbon Source-dependent Modulation Of Nadp-gdhsmentioning

confidence: 99%

“…The inter-proton distance between two carboxyl groups of isophthalate and glutamate is 7.45 Å (0.745 nm), which makes isophthalate a potent competitive inhibitor of GDH compared with phthalate and terephthalate (Caughey et al, 1957). Isophthalic acid and its derivatives have been reported to inhibit NAD-dependent GDH (NAD-GDH) from bovine, fungal, yeast and pea plant sources (Boots et al, 1976;Caughey et al, 1957;Cunliffe et al, 1983;Rogers et al, 1972;Stevens et al, 1989), as well as NADP-dependent GDH (NADP-GDH) from Aspergillus niger (Noor & Punekar, 2005). GDH (EC 1.4.1.2-4) plays a crucial role at the crossroads of carbohydrate and amino acid metabolism.…”

Section: Introductionmentioning

confidence: 99%

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

2008

Microbiology

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 a-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 NADPdependent GDH (NADP-GDH), while cells grown on glucose, 2¾ 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 sourcedependent 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.