The determination of reduced nicotinamide-adenine dinucleotide and metabolic intermediates in picomole amounts with bacterial luciferase

A continuous spectrophotometric assay for monitoring adenosine 5'-monophosphate production

A number of biologically important enzymes release adenosine 5'-monophosphate (AMP) as a product, including aminoacyl-tRNA synthetases, cyclic AMP (cAMP) phosphodiesterases, ubiquitin and ubiquitin-like ligases, DNA ligases, coenzyme A (CoA) ligases, polyA deadenylases, and ribonucleases. In contrast to the abundance of assays available for monitoring the conversion of adenosine 5'-triphosphate (ATP) to ADP, there are relatively few assays for monitoring the conversion of ATP (or cAMP) to AMP. In this article, we describe a homogeneous assay that continuously monitors the production of AMP. Specifically, we have coupled the conversion of AMP to inosine 5'-monophosphate (IMP) (by AMP deaminase) to the oxidation of IMP (by IMP dehydrogenase). This results in the reduction of oxidized nicotine adenine dinucleotide (NAD(+)) to reduced nicotine adenine dinucleotide (NADH), allowing AMP formation to be monitored by the change in the absorbance at 340 nm. Changes in AMP concentrations of 5 μM or more can be reliably detected. The ease of use and relatively low expense make the AMP assay suitable for both high-throughput screening and kinetic analyses.

Bioluminescent enzyme assay for the indication of plant stress in enclosed life support systems

The application of bioluminescent sensors for monitoring key metabolites and enzymes that are indicators of stress in plants is demonstrated. The sensitivity of bioluminescent assay for NAD(P)H and NAD(P)(+) was about 0.5 and 1 nmol, respectively. The levels of NAD(P)H and NAD(P)(+) in radish (Raphanus sativus) root extracts from controls and from stress-induced conditions were compared. To induce environmental stress, the plants were grown in enclosed environmental chambers with low pressure (9 or 32 kPa), high humidity (>80%) and low oxygen partial pressure (down to 3.3-6.5 kPa). The concentrations of NAD(P)(+) and NAD(P)H in plants varied under stress conditions. Decreasing both total pressure from 101.5 to 32 or 9 kPa and partial pressure of oxygen increased the ratio of NAD(P)(+) /NAD(P)H from 0.2 to 4 or 6, respectively. The increase in this ratio suggests that plants are undergoing stress in these hypobaric environments. The developed bioluminescent assay for quantification of pyridine nucleotides in plant tissues is rapid, low-cost and easily performed.

Metabolism in perfused rat lived at different terms after short-term hyperthermia

The metabolic state of rat liver was studied in vivo 1, 6, and 18 h after single hyperthermia (42 degrees C). It was shown that intracellular compensatory reactions involved in restoration of the energy state and realization of endogenous cytoprotective mechanisms play a role during recovery.

Top-down control analysis of ATP turnover, glycolysis and oxidative phosphorylation in rat hepatocytes

Control analysis was used to analyse the internal control of rat hepatocyte metabolism. The reactions of the cell were grouped into nine metabolic blocks linked by five key intermediates. The blocks were glycogen breakdown, glucose release, glycolysis, lactate production, NADH oxidation, pyruvate oxidation, mitochondrial proton leak, mitochondrial phosphorylation and ATP consumption. The linking intermediates were intracellular glucose-6-phosphate, pyruvate and ATP levels, cytoplasmic NADH/NAD ratio and mitochondrial membrane potential. The steady-state fluxes through the blocks and the levels of the intermediates were measured in the absence and presence of specific effectors of hepatocyte metabolism. Application of the multiple modulation approach gave the kinetic responses of each block to each intermediate (the elasticities). These were then used to calculate all of the control coefficients, which describe the degree of control each block had over the level of each intermediate, and over the rate of each process. Within this full description of control, many different interactions could be identified. One key finding was that the processes that consumed ATP had only 35% of the control over the rate of ATP consumption. Instead, the reactions that produced ATP exerted the most control over ATP consumption rate; particularly important were mitochondrial phosphorylation (30% of control) and glycolysis (19%). The rate of glycolysis was positively controlled by the glycolytic enzymes themselves (66% of control) and by ATP consumption (47%). Mitochondrial production of ATP, including oxidative, proton leak and phosphorylation processes, had negative control over glycolysis (-26%; the Pasteur effect). In contrast, glycolysis had little control over the rate of ATP production by the mitochondria (-10%; the Crabtree effect). Control over the flux through the mitochondrial phosphorylation block was shared between pyruvate oxidation (23%), ATP consumption (28%) and the mitochondrial phosphorylation block itself (64%).

Rapid changes in oxidative metabolism as a consequence of elicitor treatment of suspension-cultured cells of French bean (Phaseolus vulgaris L.)

Stressed plant cells often show increased oxygen uptake which can manifest itself in the transient production of active oxygen species, the oxidative burst. There is a lack of information on the redox status of cells during the early stages of biotic stress. In this paper we measure oxygen uptake and the levels of redox intermediates NAD/NADH and ATP and show the transient induction of the marker enzyme for redox stress, alcohol dehydrogenase. Rapid changes in the redox potential of elicitor-treated suspension cultures of French bean cells indicate that, paradoxically, during the period of maximum oxygen uptake the levels of ATP and the NADH/NAD ratio fall in a way that indicates the occurrence of stress in oxidative metabolism. This period coincides with the maximum production of active oxygen species particularly H2O2. The cells recover and start producing ATP immediately of H2O2 production. This indicates that the increased O2 uptake is primarily incorporated into active O2 species. A second consequence of these changes is probably a transient compromising of the respiratory status of the cells as indicated in expression of alcohol dehydrogenase. Elicitor-induced bean ADH was purified to homogeneity and the M(r) 40,000 polypeptide was subjected to amino acid sequencing. 15% of the whole protein was sequenced from three peptides and was found to have nearly 100% sequence similarity to the amino acid sequence for pea ADH1 (PSADH1). The cDNA coding for the pea enzyme was used to demonstrate the transient induction of ADH mRNA in elicitor-treated bean cells. Enzyme activity levels also increased transiently subsequently. Increased oxygen uptake has previously been thought to be associated with provision of energy for the changes in biosynthesis that occur rapidly after perception of the stress signal. However the present work shows that this rapid increase in oxygen uptake as a consequence of elicitor action is not wholly associated with respiration.

Glycogen breakdown in cleaving Xenopus embryos is limited by ADP

Xenopus eggs contain large stores of glycogen, but this glycogen is not glycolytically processed during cleavage. The Embden-Meyerhof pathway is inhibited by the absence of pyruvate kinase activity in vivo, and lactate and pyruvate are present at relatively low levels. In the late blastula, just preceding gastrulation, lactate levels increase, indicating the onset of glycogen breakdown and glycolytic flux. Glycolysis from microinjected [14C]glucose-6-phosphate could be transiently activated, however, by the coinjection of ADP into fertilized eggs, and constitutively activated by the injection of the ATPase potato apyrase, indicating the presence of all enzymes necessary for glycolytic activity. The isozyme profiles of pyruvate kinase and malic enzyme, two enzymes involved in carbon metabolism during cleavage or in the subsequent activation of glycogen breakdown, do not change between the egg and gastrula stages. These data suggest that the activation of glycogen breakdown and glycolysis in the late blastula is probably not a result of new gene activity but may be the metabolic consequence of increased free ADP that is then able to support the pyruvate kinase reaction.

Glutamate and GABA levels in CSF from patients affected by dementia and olivo-ponto-cerebellar atrophy

The modifications in the CSF content of glutamate and GABA in patients afflicted with primary degenerative dementia (PDD) and olivo-ponto-cerebellar atrophy (OPCA) have been evaluated. Control subjects (with disk herniation) were also included in the study. The amino-acids assays were carried out utilizing enzymatic-bioluminescence technique. GABA levels in controls were 803 +/- 98 (n = 7) and in demented patients 702 +/- 98 (n = 7) pmol/ml. Glutamate levels were 2067 +/- 244 (n = 10) in controls, 1190 +/- 81 (n = 16) pmol/ml (vs controls p less than 0.01) in demented patients, and 1116 +/- 146 (vs controls p less than 0.01) in OPCA patients. These results suggest that CSF glutamate levels in severely demented patients might be a result of generalized neuronal loss in the brain with a reactive gliosis.

Time course changes in glycogen accretion, 6-phosphogluconate, fructose-2,6-bisphosphate, and lipogenesis upon refeeding a high sucrose diet to starved rats

1. Starved rats refed 60% sucrose diets were used to determine in vivo lipogenesis and levels of hepatic metabolites. 2. Fatty acid synthesis increased 11-fold 4 hr after refeeding. 3. Glycogen rose from 3 to 100 mg/g liver after 8 hr. 4. Fructose-2,6-bisphosphate rose to 6 nmol/g at 1 hr and remained constant. 5. 6-Phosphogluconate increased from 10 to 45 nmol/g liver after 2 hr and remained constant.

Effect of 6-aminonicotinamide on pentose cycle activity in isolated hepatocytes

1. 6-aminonicotinamide (6AN), a purported inhibitor of 6-phosphogluconate (6PG) dehydrogenase, has been regarded as an inhibitor of the pentose cycle. 2. Incubation of isolated hepatocytes with 6AN caused a time- and concentration-dependent accumulation of 6PG. 3. At 5 mM, 6AN increased the 6PG level 1000-times to values comparable to those observed in the livers of rats injected with this niacin antagonist. 4. Despite the accumulation of 6PG, neither the total rate of lipogenesis, nor the incorporation of radioactivity from [3-3H]glucose, used to estimate the activity of the pentose cycle, were impaired to a large extent. 5. The evidence presented suggests that the accumulation of 6PG is not a sufficient criterion to establish blockade of the pentose cycle.

Determination of intracellular pyridine nucleotide levels by bioluminescence using anaerobic bacteria as a model

An assay for the determination of NAD(P)+ and NAD(P)H in extracts from the obligate anaerobe bacterium Thermoanaerobacter finnii is developed and the strategy for this development is described. This assay performed with constant FMN reductase (EC 1.6.8.1) and luciferase (EC 1.14.14.3) concentrations has been shown to detect as low as 1 pmol pyridine nucleotide. With this assay recovery, efficiency of extraction, reliability, and detection limit of the procedures were determined. To our knowledge this is the first bioluminometric assay for the determination of pyridine nucleotide levels in bacterial extracts.

Enzymatic assay for 3-hydroxyacyl-CoA and 2-trans-enoyl-CoA intermediates of beta-oxidation

An enzymatic assay is presented for determining 3-hydroxyacyl-CoA and 2-trans-enoyl-CoA esters in tissue samples. The procedure includes extraction of acyl-CoA esters from frozen tissue samples with chloroform/methanol, stochiometric oxidation of the acyl esters to 3-keto-acyl-CoAs with 3-hydroxyacyl-CoA dehydrogenase in the presence or absence of enoyl-CoA hydratase, and an enzymatic cycling amplification of NADH produced for fluorometric determination. The procedure allows measurement of these intermediates of beta-oxidation at the picomole level. The method has been used successfully to measure the concentrations of 3-hydroxyacyl-CoA and 2-trans-enoyl-CoA esters in isolated rat hearts perfused with glucose or oleate or under anoxia.

Possible role for the glucose-fatty acid cycle in dexamethasone-induced insulin antagonism in rats

This study was undertaken to elucidate the mechanism(s) involved in glucocorticoid-induced insulin antagonism. Male Sprague-Dawley rats (200 to 210 g) were injected with 1 mg/kg dexamethasone-phosphate (Dex) or the vehicle every other day for 10 days. Two days after the last injection, fasted anesthetized animals were infused (per kg body weight per min) with 8 mg glucose, 5 mU porcine insulin and 1.4 micrograms somatostatin with blood sampling before, and at 10 min intervals between 90 and 130 min after the pancreatic suppression test was begun. At the end of the test, abdominal muscle was quickly freeze-clamped and the substrate and products of the rate-determining reactions of glycolysis and glycogenesis were measured. Dex-treated rats had higher basal (0 min) and steady-state levels (90-130 min) of both glucose and insulin signifying insulin antagonism. The pattern of muscle tissue metabolites revealed no free intracellular glucose in either group and concentrations of all other metabolites in the Dex-treated rats were less than those in the control animals (except for a small increase in glycogen). These results suggest a site of insulin antagonism between (and including) insulin binding and glucose transport. Further studies in the Dex-treated rats revealed normal: a) insulin binding to freshly isolated hepatocytes; b) basal and insulin-stimulated xylose transport in soleus muscle; c) basal and insulin-stimulated glucose uptake in hemidiaphragms. These normal in-vitro results suggested that a circulating factor may be responsible. Repeat pancreatic suppression tests in the Dex-treated rats revealed blunted suppression of serum FFA concentrations.(ABSTRACT TRUNCATED AT 250 WORDS)

Quantitative analysis of intermediary metabolism in hepatocytes incubated in the presence and absence of glucagon with a substrate mixture containing glucose, ribose, fructose, alanine and acetate

Hepatocytes were isolated from the livers of fed rats and incubated, in the presence and absence of 100 nM-glucagon, with a substrate mixture containing glucose (10 mM), fructose (4 mM), alanine (3.5 mM), acetate (1.25 mM), and ribose (1 mM). In any given incubation one substrate was labelled with 14C. Incorporation of 14C into glucose, glycogen, CO2, lactate, alanine, glutamate, lipid glycerol and fatty acids was measured after 20 and 40 min of incubation under quasi-steady-state conditions [Borowitz, Stein & Blum (1977) J. Biol. Chem. 252, 1589-1605]. These data and the measured O2 consumption were analysed with the aid of a structural metabolic model incorporating all reactions of the glycolytic, gluconeogenic, and pentose phosphate pathways, and associated mitochondrial and cytosolic reactions. A considerable excess of experimental measurements over independent flux parameters and a number of independent measurements of changes in metabolite concentrations allowed for a stringent test of the model. A satisfactory fit to the data was obtained for each condition. Significant findings included: control cells were glycogenic and glucagon-treated cells glycogenolytic during the second interval; an ordered (last in, first out) model of glycogen degradation [Devos & Hers (1979) Eur. J. Biochem. 99, 161-167] was required in order to fit the experimental data; the pentose shunt contributed approx. 15% of the carbon for gluconeogenesis in both control and glucagon-treated cells; net flux through the lower Embden-Meyerhof pathway was in the glycolytic direction except during the 20-40 min interval in glucagon-treated cells; the increased gluconeogenesis in response to glucagon was correlated with a decreased pyruvate kinase flux and lactate output; fluxes through pyruvate kinase, pyruvate carboxylase, and phosphoenolpyruvate carboxykinase were not coordinately controlled; Krebs cycle activity did not change with glucagon treatment; flux through the malic enzyme was towards pyruvate formation except for control cells during interval II; and 'futile' cycling at each of the five substrate cycles examined (including a previously undescribed cycle at acetate/acetyl-CoA) consumed about 26% of cellular ATP production in control hepatocytes and 21% in glucagon-treated cells.

A sensitive kinetic assay for glycerol using bacterial bioluminescence

A kinetic assay method based on bacterial bioluminescence and the glycerol dehydrogenase (GDH) enzyme reaction has been developed for the determination of glycerol. The assay system involves the use of three coupled enzyme reactions in which the participating reactants are optimized to allow internal calibration by known amounts of glycerol. This bioluminescent assay method is also suitable for measuring GDH enzyme activity. The lower detection limit for glycerol is 500 pmol and for GDH, 0.001 mU, the assay being linear up to 300 nmol of glycerol and 3 mU of GDH. The percentage recovery of glycerol from serum was 95-100%. This assay method is rapid, sensitive, and reproducible.

The analysis of picomole amounts of L(+)- and D(-)-lactic acid in samples of dental plaque using bacterial luciferase

L(+)-Lactic acid (5 pmol) and D(-)-lactic acid (20 pmol) were assayed by coupling the generation of NADH with the use of bacterial luciferase. The binding of NADH to L(+)-lactic dehydrogenase made it necessary to denature the protein so that the assay with bacterial luciferase was effective. The coupled luciferase assay of L(+)-lactic acid was 400 times more sensitive than the fluorometric assay. The luciferase coupled assay was used to analyze the L(+)- and D(-)-lactic acid contents of small samples of dental plaque.

Quantitative analysis of flux along the gluconeogenic, glycolytic and pentose phosphate pathways under reducing conditions in hepatocytes isolated from fed rats

Hepatocytes were isolated from the livers of fed rats and incubated with a mixture of glucose (10 mM), ribose (1 mM), mannose (4 mM), glycerol (3 mM), acetate (1.25 mM), and ethanol (5 mM) with one substrate labelled with 14C in any given incubation. Incorporation of label into CO2, glucose, glycogen, lipid glycerol and fatty acids, acetate and C-1 of glucose was measured at 20 and 40 min after the start of the incubation. The data (about 48 measurements for each interval) were used in conjunction with a single-compartment model of the reactions of the gluconeogenic, glycolytic and pentose phosphate pathways and a simplified model of the relevant mitochondrial reactions. An improved method of computer analysis of the equations describing the flow of label through each carbon atom of each metabolite under steady-state conditions was used to compute values for the 34 independent flux parameters in this model. A good fit to the data was obtained, thereby permitting good estimates of most of the fluxes in the pathways under consideration. The data show that: net flux above the level of the triose phosphates is gluconeogenic; label in the hexose phosphates is fully equilibrated by the second 20 min interval; the triose phosphate isomerase step does not equilibrate label between the triose phosphates; substrate cycles are operating at the glucose-glucose 6-phosphate, fructose 6-phosphate-fructose 1,6-bisphosphate and phosphoenolpyruvate-pyruvate-oxaloacetate cycles; and, although net flux through the enzymes catalysing the non-oxidative steps of the pentose phosphate pathway is small, bidirectional fluxes are large.

Microdetermination of glycerol using bacterial NADH-linked luciferase

A bioluminescent assay for determination of glycerol using bacterial NADH-linked luciferase was developed and successfully applied to measurement of glycerol release from human fat cells. The procedure is based on enzymic conversion of glycerol to 3-phosphoglycerate, which is irreversible in the presence of arsenate, and subsequent determination of NADH formed in the glycerol-phosphate- and glyceraldehyde-3-phosphate dehydrogenase reactions respectively. Bioluminescent determination of glycerol is about 100 times more sensitive than conventional spectrophotometry, thus permitting more than 100 determinations to be carried out on needle biopsy specimens.