A comparative study of the glutamate dehydrogenase activity in several species of marine phytoplankton

Ahmed, S. I.; Kenner, R. A.; Packard, Theodore T.

doi:10.1007/bf00395598

Cited by 24 publications

(8 citation statements)

References 14 publications

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“…GS activity was assayed by the y-glutamyl transferase (GT) reaction (Shapiro & Stadtrnan 1970, Bender et al 1977, which estimates total enzyme activity regardless of subunit adenylation state (Mn2+ dependent activity). GDH activity was measured by the fluorometric detection of nicotinamide adenine dinucleotide (phosphate) [NAD(P)+] (Ahmed et al 1977).…”

Section: Methodsmentioning

confidence: 99%

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Relations between bacterial nitrogen metabolism and growth efficiency in an estuarine and an open-water ecosystem

Jørgensen¹,

Kroer²,

Coffin³

et al. 1999

Aquat. Microb. Ecol.

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Bacterial uptake or release of dissolved nitrogen compounds (amino nitrogen, urea, ammonium and nitrate) were examined in 0.8 pm filtered water from an estuary (Santa Rosa Sound [SRS], northwestern Florida) and an open-water location in the Gulf of Mexico (GM). The bacterial nutrient dynamics were related to oxygen consumption and activity of enzymes involved in nitrogen assimilation (glutamate dehydrogenase [GDH], glutamine synthetase [GS] and aminopeptidase activity [leu-MCA]). Dissolved free amino acids (DFAA) were the dominant N source to the bacteria, followed by dissolved combined amino acids (DCAA), ammonium and nitrate. Nitrogen budgets of the bacteria (assimilation of N compounds relative to accumulated N biomass) demonstrated that, except for the initial 24 h period in the GM cultures, the assimilated N compounds sustained all of the bacterial N demand. Urea was released in both sets of cultures, but in the SRS cultures the produced urea was reassimilated. Major differences in the bacterial N metabolism between the open-water GM and the estuarine SRS stations were observed. Relative to the GM station, bacteria in the SRS cultures had (1) a 2.4 to 18x higher cell-specific DFAA assimilation, (2) a 2 . 5~ higher cell-specific leu-MCA activity, (3) a 3 to 10x higher GDH:GS activity ratio and (4) a 1.9 to 4 . 1~ lower cell-specific respiration. The larger nutrient availability at the estuarine station probably caused these differences in uptake and metabolism of nitrogen as well as the lower respiratory rate, relative to the open-water station. Therefore, we hypothesize that availability of nitrogen, rather than carbon, controlled the bacterial activity in the cultures. Our results suggest that bacteria in eutrophic conditions can be more important mediators of nitrogen than those in oligotrophic conditions, in which bacteria temporarily may immobilize labile nitrogen.

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Section: Methodsmentioning

confidence: 99%

“…Reactions were stopped by acidification with GT 'stop-mix' for GS assays (Bender et ai. 1977) and 0.1 N HC1 for the GDH assays (Ahmed et al 1977). The concentration of y-glutamyl hydroxamate (GH) in GS assays was determined at 540 nm absorption immediately after centrifuging precipitates and filter material.…”

Section: Methodsmentioning

confidence: 99%

Relations between bacterial nitrogen metabolism and growth efficiency in an estuarine and an open-water ecosystem

Jørgensen¹,

Kroer²,

Coffin³

et al. 1999

Aquat. Microb. Ecol.

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“…Therefore, at substrate saturating conditions, we assume that GT activity is proportional to GS protein content (expression) for all possible isozymes. GDH isozymes were assayed as the biosynthetic activity, i.e., reductive amination activity, by the fluorometric detection of oxidized nicotinamide adenine dinucleotide (phosphate), NAD(P) + (Ahmed et al 1977). Activity dependent on NADPH is referred to as anabolic GDH (GDH A ) and that dependent on NADH is referred to as catabolic GDH (GDH C ).…”

Section: Materials and Proceduresmentioning

confidence: 99%

“…NAD(P)H was made fresh daily in 0.1 M carbonate-bicarbonate buffer (pH 10.6). This alkaline solution was boiled 3 min to destroy oxidized forms (NAD(P) + ) then cooled on ice prior to use in assays (Ahmed et al 1977). Assays were incubated at 30°C for 30 to 60 min and terminated with 0.5 mL 1.2 N HCl.…”

Section: Materials and Proceduresmentioning

confidence: 99%

“…Activities of GS and GDH have been measured in a few studies of N metabolism in natural phytoplankton communities (Ahmed et al 1977;Dorch et al 1985; Clayton and Ahmedlatter study, bacterioplankton in seawater cultures from a more N replete estuary had about 10-fold greater GDH and repressed GS compared with cultures from an N deplete openocean site. Although, there was agreement between these enzymatic results and other parameters of N bioavailability and metabolism in these incubation experiments, no controlled experiments were performed to test assumptions on conditions controlling enzyme activities nor were optimal enzyme assay conditions presented.…”

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confidence: 99%

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Expression of glutamine synthetase and glutamate dehydrogenase by marine bacterioplankton: Assay optimizations and efficacy for assessing nitrogen to carbon metabolic balance in situ

Hoch¹,

Snyder²,

Jeffrey³

et al. 2006

Limnology & Ocean Methods

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Expression of glutamate metabolism enzymes, glutamate dehydrogenase (GDH), and glutamine synthetase (GS) are proposed to yield information on the nitrogen (N) to carbon (C) metabolic balance within bacterioplankton communities. Whole-cell assay conditions were optimized, and reactions were linear with time and biomass. Enzyme activities were assayed in seawater cultures from four ecosystems of contrasting trophic state amended with different regimes of glucose, amino acids, and ammonium (NH 4 + ) to validate expression patterns of GDH and GS in various combinations of N and C limitation or excess. In three of four experiments, glucose amendment enhanced GS expression by 2-fold but repressed GDH by 10% to 40% relative to the control. In contrast, addition of amino acids or NH 4 + resulted in 20% to 90% repression of GS and enhanced GDH expression by 20% to 900%. The GDH:GS activity ratio (×10 -3 ) ranged from 6 to 22 in glucose added treatments and 63 to 264 in NH 4 + -amended treatments and appears to be a more sensitive index of bacterial N bioavailability relative to C supply than either enzyme alone. Cluster analysis was used to identify the condition of ambient bacterioplankton by matching enzyme expression with the validation results. This enzymatic approach overcomes some of the biases and limitations of other methods for assessing N metabolism in marine bacteria while providing unique information to further understand constraints of bacterioplankton respiration, production, and N flux.

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Isotope Fractionation during Primary Production

Fogel

Cifuentes

1993

Topics in Geobiology

324

293

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A comparative study of the glutamate dehydrogenase activity in several species of marine phytoplankton

Cited by 24 publications

References 14 publications

Relations between bacterial nitrogen metabolism and growth efficiency in an estuarine and an open-water ecosystem

Relations between bacterial nitrogen metabolism and growth efficiency in an estuarine and an open-water ecosystem

Expression of glutamine synthetase and glutamate dehydrogenase by marine bacterioplankton: Assay optimizations and efficacy for assessing nitrogen to carbon metabolic balance in situ

Isotope Fractionation during Primary Production

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