Rapid evaluation of PHD2 inhibitory activity of natural products based on capillary electrophoresis online stacking strategy

Prolyl hydroxylase domain 2 (PHD2) is an important enzyme in the human body that perceives changes in oxygen concentration and regulates response in hypoxic environments. Evaluation of PHD2 inhibitory activity of natural products is crucial for drug development of hypoxia related diseases. At present, the detection of low concentration of α-ketoglutaric acid (the substrate of PHD2 enzymatic reaction) requires derivatization reactions or sample pretreatment, which undoubtedly increases the workload of PHD2 inhibitory activity evaluation. In this paper, a direct detection approach of α-ketoglutaric acid was established by using the online stacking strategy of capillary electrophoresis to evaluate the PHD2 inhibitory activity of natural products. Under optimized conditions, detection of a single sample can be achieved within 2 min. By calculation, the intraday precision RSD of the apparent electrophoretic mobility and peak areas of α-ketoglutaric acid are 0.92 % and 0.79 %, respectively, and the interday RSD were 1.27 % and 0.96 % respectively. The recoveries of the present approach were 97.9-105.2 %, and the LOQ and LOD were 2.0 μM and 5.0 μM, respectively. Furthermore, this approach was applied for the evaluation of inhibitory activity of PHD2 for 13 natural products, and PHD2 inhibitory activity of salvianolic acid A was firstly reported. The present work not only realizes evaluation of PHD2 inhibitory activity through direct detection of α-ketoglutaric acid, but also provides technical support for the discovery of potential drug molecules in hypoxia related diseases.

A Stereoselective Strigolactone Biosynthesis Catalyzed by a 2-Oxoglutarate-Dependent Dioxygenase in Sorghum

Seeds of root parasitic plants, Striga, Orobanche and Phelipanche spp., are induced to germinate by strigolactones (SLs) exudated from host roots. In Striga-resistant cultivars of Sorghum bicolor, the loss-of-function of the Low Germination Stimulant 1 (LGS1) gene changes the major SL from 5-deoxystrigol (5DS) to orobanchol, which has an opposite C-ring stereochemistry. The biosynthetic pathway of 5DS catalyzed by LGS1 has not been fully elucidated. Since other unknown regulators, in addition to LGS1 encoding a sulfotransferase, appear to be necessary for the stereoselective biosynthesis of 5DS, we examined Sobic.005G213500 (Sb3500), encoding a 2-oxoglutarate-dependent dioxygenase, as a candidate regulator, which is co-expressed with LGS1 and located 5'-upstream of LGS1 in the sorghum genome. When LGS1 was expressed with known SL biosynthetic enzyme genes including the cytochrome P450 SbMAX1a in Nicotiana benthamiana leaves, 5DS and its diastereomer 4-deoxyorobanchol (4DO) were produced in approximately equal amounts, while the production of 5DS was significantly larger than that of 4DO when Sb3500 was also co-expressed. We also confirmed the stereoselective 5DS production in an in vitro feeding experiment using synthetic chemicals with recombinant proteins expressed in Escherichia coli and yeast. This finding demonstrates that Sb3500 is a stereoselective regulator in the conversion of the SL precursor carlactone to 5DS, catalyzed by LGS1 and SbMAX1a, providing a detailed understanding of how different SLs are produced to combat parasitic weed infestations.

A high-throughput SAMDI-mass spectrometry assay for isocitrate dehydrogenase 1

The enzyme isocitrate dehydrogenase 1 (IDH1) catalyzes the conversion of isocitrate to alpha-ketoglutarate (αKG) and has emerged as an important therapeutic target for glioblastoma multiforme (GBM). Current methods for assaying IDH1 remain poorly suited for high-throughput screening of IDH1 antagonists. This paper describes a high-throughput and quantitative assay for IDH1 that is based on the self-assembled monolayers for matrix-assisted laser desorption/ionization-mass spectrometry (SAMDI-MS) method. The assay uses a self-assembled monolayer presenting a hydrazide group that covalently captures the αKG product of IDH1, where it can then be detected by MALDI-TOF mass spectrometry. Co-capture of an isotopically-labeled αKG internal standard allows the αKG concentration to be quantitated. The assay was used to analyze a series of standard αKG solutions and produced minimal error in measured αKG concentration values. The suitability of the assay for high-throughput analysis was evaluated in a 384-sample biochemical IDH1 screen. Cells expressing IDH1 were lysed and the lysate was applied to the monolayer to capture αKG, which was then quantitated using the SAMDI-MS assay. Cells in which IDH1 expression was reduced by small-interfering RNA exhibited a corresponding decrease in αKG concentration as measured by the assay. Application of the assay toward the high-throughput screening of IDH1 inhibitors or knockdown agents may facilitate the discovery of treatments for GBM.

Citric Acid Metabolism in Resistant Hypertension: Underlying Mechanisms and Metabolic Prediction of Treatment Response

Resistant hypertension (RH) affects 9% to 12% of hypertensive adults. Prolonged exposure to suboptimal blood pressure control results in end-organ damage and cardiovascular risk. Spironolactone is the most effective drug for treatment, but not all patients respond and side effects are not negligible. Little is known on the mechanisms responsible for RH. We aimed to identify metabolic alterations in urine. In addition, a potential capacity of metabolites to predict response to spironolactone was investigated. Urine was collected from 29 patients with RH and from a group of 13 subjects with pseudo-RH. For patients, samples were collected before and after spironolactone administration and were classified in responders (n=19) and nonresponders (n=10). Nuclear magnetic resonance was applied to identify altered metabolites and pathways. Metabolites were confirmed by liquid chromatography-mass spectrometry. Citric acid cycle was the pathway most significantly altered (P<0.0001). Metabolic concentrations were quantified and ranged from ng/mL malate to μg/mL citrate. Citrate and oxaloacetate increased in RH versus pseudoresistant. Together with α-ketoglutarate and malate, they were able to discriminate between responders and nonresponders, being the 4 metabolites increased in nonresponders. Combined as a prediction panel, they showed receiver operating characteristiccurve with area under the curve of 0.96. We show that citric acid cycle and deregulation of reactive oxygen species homeostasis control continue its activation after hypertension was developed. A metabolic panel showing alteration before spironolactone treatment and predicting future response of patients is shown. These molecular indicators will contribute optimizing the rate of control of RH patients with spironolactone.

Comparative genomics analysis of a series of Yarrowia lipolytica WSH-Z06 mutants with varied capacity for α-ketoglutarate production

Yarrowia lipolytica is one of the most intensively investigated α-ketoglutaric acid (α-KG) producers, and metabolic engineering has proven effective for enhancing production. However, regulation of α-KG metabolism remains poorly understood. Genetic engineering of new strains is accompanied by potential safety concerns in some countries and regions. A series of mutants with varied capacity for α-KG production were obtained using random mutagenesis of Y. lipolytica WSH-Z06. Comparative genomics analysis was implemented to identify genes candidates associated with α-KG production. Manipulation of genes regulating mitochondrial biogenesis and energy metabolism could improve α-KG production, while genes involved in regulating transformation between keto acids and amino acids may decrease production. One gene associated with cell cycle control well represented in all mutants, whereas this gene involved in cell concentration do not appear to influence α-KG production. The results shed light on α-KG production in eukaryotic cells, and pave the way for a high-throughput screening and random mutagenesis method for enhancing α-KG production.

α-ketoglutarate is associated with delayed wound healing in diabetes

AIM

A high level of matrix metalloproteinase 9 (MMP-9) is a predictor of poor wound healing in diabetic foot ulcers. In skin keratinocytes, site-specific DNA demethylation plays an important role in MMP-9 expression. Ten-eleven translocation enzyme 2 (TET2) protein, one member of TET family, could rely on α-ketoglutarate (α-KG) as cosubstrate to exhibit catalytic activity of DNA demethylation. Here, we aimed to explore the changes of α-KG and its relationship with MMP-9 and TET2 during diabetic wound healing.

METHODS

Seventy-one cases of patients with diabetic foot ulcers and 53 cases of nondiabetic ulcers were enrolled. Serum, urine and wound fluids were collected for measurement of α-KG levels and MMP-9 expression. Skin tissues were collected for the measurement of TET2 and MMP-9 expression. Clinical parameters were collected, and transcutaneous oxygen pressure (TcPO2) levels of feet were detected.

RESULTS

The levels of α-KG, TET2 and MMP-9 were significantly increased in diabetic wound compared with nondiabetic wound (P = 0·010, 0·016 and 0·025). There was a significant correlation between a low TcPO2 and a high α-KG level of wound fluids (r = -0·395, P = 0·002). Further analysis showed that α-KG concentration had a positive correlation with both haemoglobin A1c (HbA1C) and 2 h postprandial blood glucose (PBG) (r = 0·393, P = 0·005; r = 0·320, P = 0·025, respectively).

CONCLUSIONS

The levels of α-KG, TET2 and MMP-9 were significantly increased in diabetic wound compared with nondiabetic wound. Elevated α-KG was related to local hypoxia ischaemia status and systematic poor glycaemic control.

Effect of cluster thinning and prohexadione calcium applications on phenolic composition and sensory properties of red wines

The overall objective of this study was to investigate the effect of manual cluster thinning (CT) and the application of the growth regulator Prohexadione calcium (ProCa) on the phenolic composition and the sensory profile of Tempranillo and Grenache wines produced from treated vines in La Rioja (Spain). ProCa was applied at preblooming and CT was carried out at veraison in two consecutive years. Different physicochemical parameters and analyses of phenolic compounds were carried out in control, CT and ProCa grapes and wines and wine sensory was performed. Thinning treatments decreased crop yield, besides ProCa application reduced berry size, and berry weight. Color and phenolic composition of Grenache and Tempranillo wines in general were affected by thinning treatments, with an increase in anthocyanin, flavanol and flavonol concentrations. In sensory analysis, wines obtained from thinned vines presented higher values for several aromatic (e.g., white and yellow fruits, fresh flowers) and taste attributes (i.e., astringency, bitternes, persistence). CT and ProCa treatments resulted in an improvement in wine quality. In general, similar results in phenolic composition, sensory properties and quality of wines were obtained by manual and chemical cluster thinning. ProCa as a growth regulator may be an option for a quality vitiviniculture.

Theoretical analysis of carbon-13 magnetization transfer for in vivo exchange between alpha-ketoglutarate and glutamate

Many enzymes catalyze fast exchange between a small pool and a large pool in vivo. For example, aspartate aminotransferase catalyzes fast exchanges between alpha-ketoglutarate and glutamate and between oxaloacetate and aspartate, which can be detected using in vivo(13)C MRS while saturating alpha-carbons of the keto acids. Unlike in the traditional saturation transfer experiments studied using (31)P MRS, the tricarboxylic acid cycle intermediates alpha-ketoglutarate and oxaloacetate are below the detection limit of in vivo NMR. In this work, a theoretical analysis of the saturation transfer between alpha-ketoglutarate and glutamate catalyzed by aspartate aminotransferase was presented to examine the requirements for complete saturation of the rapidly turning over alpha-ketoglutarate pool without affecting the longitudinal magnetization of glutamate. The fast turnover of the small alpha-ketoglutarate pool also allows a quasi-steady-state approximation of its dynamic longitudinal relaxation. The theoretical analysis provides a useful guide for designing experimental methods to characterize saturation transfer processes associated with fast turning over small pools in vivo.

PII signal transduction proteins: sensors of alpha-ketoglutarate that regulate nitrogen metabolism

PII proteins are small homotrimeric signal transduction proteins that regulate the activities of metabolic enzymes and permeases, and control the activities of signal transduction enzymes. The protein family shows high conservation, with examples in eukaryota (plants and eukaryotic algae), archaea, and bacteria. This distribution indicates that PII is one of the most ancient signalling proteins known.

Statistical total correlation spectroscopy: an exploratory approach for latent biomarker identification from metabolic 1H NMR data sets

We describe here the implementation of the statistical total correlation spectroscopy (STOCSY) analysis method for aiding the identification of potential biomarker molecules in metabonomic studies based on NMR spectroscopic data. STOCSY takes advantage of the multicollinearity of the intensity variables in a set of spectra (in this case 1H NMR spectra) to generate a pseudo-two-dimensional NMR spectrum that displays the correlation among the intensities of the various peaks across the whole sample. This method is not limited to the usual connectivities that are deducible from more standard two-dimensional NMR spectroscopic methods, such as TOCSY. Moreover, two or more molecules involved in the same pathway can also present high intermolecular correlations because of biological covariance or can even be anticorrelated. This combination of STOCSY with supervised pattern recognition and particularly orthogonal projection on latent structure-discriminant analysis (O-PLS-DA) offers a new powerful framework for analysis of metabonomic data. In a first step O-PLS-DA extracts the part of NMR spectra related to discrimination. This information is then cross-combined with the STOCSY results to help identify the molecules responsible for the metabolic variation. To illustrate the applicability of the method, it has been applied to 1H NMR spectra of urine from a metabonomic study of a model of insulin resistance based on the administration of a carbohydrate diet to three different mice strains (C57BL/6Oxjr, BALB/cOxjr, and 129S6/SvEvOxjr) in which a series of metabolites of biological importance can be conclusively assigned and identified by use of the STOCSY approach.

Krebs cycle enzymes from livers of old mice are differentially regulated by caloric restriction

Krebs cycle enzyme activities and levels of five metabolites were determined from livers of old mice (30 months) maintained either on control or on long-term caloric restriction (CR) diets (28 months). In CR mice, the cycle was divided into two major blocks, the first containing citrate synthase, aconitase and NAD-dependent isocitrate dehydrogenase which showed decreased activities, while the second block, containing the remaining enzymes, displayed increased activity (except for fumarase, which was unchanged). CR also resulted in decreased levels of citrate, glutamate and alpha-ketoglutarate, increased levels of malate, and unchanged levels of aspartate. The alpha-ketoglutarate/glutamate and malate/alpha-ketoglutarate ratios were higher in CR, in parallel with previously reported increases with CR in pyruvate carboxylase activity and glucagon levels, respectively. The results indicate that long-term CR induces a differential regulation of Krebs cycle in old mice and this regulation may be the result of changes in gene expression levels, as well as a complex interplay between enzymes, hormones and other effectors. Truncation of Krebs cycle by CR may be an important adaptation to utilize available substrates for the gluconeogenesis necessary to sustain glycolytic tissues, such as brain.

Citrate Oscillates in Liver and Pancreatic Beta Cell Mitochondria and in INS-1 Insulinoma Cells

Oscillations in citric acid cycle intermediates have never been previously reported in any type of cell. Here we show that adding pyruvate to isolated mitochondria from liver, pancreatic islets, and INS-1 insulinoma cells or adding glucose to intact INS-1 cells causes sustained oscillations in citrate levels. Other citric acid cycle intermediates measured either did not oscillate or possibly oscillated with a low amplitude. In INS-1 mitochondria citrate oscillations are in phase with NAD(P) oscillations, and in intact INS-1 cells citrate oscillations parallel oscillations in ATP, suggesting that these processes are co-regulated. Oscillations have been extensively studied in the pancreatic beta cell where oscillations in glycolysis, NAD(P)/NAD(P)H and ATP/ADP ratios, plasma membrane electrical activity, calcium levels, and insulin secretion have been well documented. Because the mitochondrion is the major site of ATP synthesis and NADH oxidation and the only site of citrate synthesis, mitochondria need to be synchronized for these factors to oscillate. In suspensions of mitochondria from various organs, most of the citrate is exported from the mitochondria. In addition, citrate inhibits its own synthesis. We propose that this enables citrate itself to act as one of the cellular messengers that synchronizes mitochondria. Furthermore, because citrate is a potent inhibitor of the glycolytic enzyme phosphofructokinase, the pacemaker of glycolytic oscillations, citrate may act as a metabolic link between mitochondria and glycolysis. Citrate oscillations may coordinate oscillations in mitochondrial energy production and anaplerosis with glycolytic oscillations, which in the beta cell are known to parallel oscillations in insulin secretion.

Role of organic acids in aluminum accumulation and plant growth in Melastoma malabathricum

Melastoma malabathricum L. (melastoma) is an Al-accumulating woody plant that grows in tropical Southeast Asia in acid soils with high aluminum (Al) concentrations and low nutrient concentrations. Because oxalate serves as a ligand for Al accumulation in melastoma leaves and citrate is the ligand associated with Al translocation from roots to shoots, we investigated the role of organic acids in the adaptation of melastoma to growth on these soils. Phosphorus starvation increased oxalate concentration in the rhizosphere, enabling melastoma to solubilize insoluble aluminum phosphate in the rhizosphere. Increased availability of P and Al in the rhizosphere enhanced growth. In the xylem sap, the concentration of citrate increased with increasing Al concentration. In contrast, the concentrations of malate, succinate and alpha-ketoglutarate in the xylem sap decreased with increasing Al concentration, suggesting that tricarboxylic acid cycle enzymes were affected by Al treatment.

Enzymatic amplification by substrate recycling for alpha-ketoglutarate in conjunction with capillary electrophoresis

The application of substrate cycling for alpha-ketoglutarate (AKG) through enzymatic amplification has been demonstrated in conjunction with capillary electrophoresis. AKG is determined using an off-line assay, which involves the coupled enzymatic reactions catalyzed by glutamate dehydrogenase and glutamic oxalacetic transaminase. Varying concentrations of the substrate and set concentrations of cofactors and enzyme are incubated together outside the CE instrument. The accumulated product, nicotinamide adenine dinucleotide, reduced form (NADH), was detected at 340 nm using CE. Amplification of a factor of 10 over just the reversed glutamate dehydrogenase reactions permitted an AKG detection limit of 10 microM. Throughput for each assay is about 5 min (including wash and equilibrium steps). After simple dilution as the only sample pretreatment, spiked AKG serum samples were determined with an average recovery of 96% with a 3% RSD.

Monitoring of alpha-ketoglutarate in a fermentation process using expanded bed enzyme reactors

A bienzyme flow injection system is presented for the monitoring of alpha-ketoglutarate produced in a fermentation process, using glutamate dehydrogenase (GDH) and glutamate oxidase (GlOx) immobilised in two serially connected expanded bed reactors. The use of expanded bed resulted in unhindered passage of the bacterial cells through the columns, and thereby the need of a separate filtering step (e.g. microdialysis) was avoided. In the first reactor, alpha-ketoglutarate was converted to L-glutamate by GDH in the presence of ammonia and NADH. In the following reactor, L-glutamate was converted by GlOx to alpha-ketoglutarate, ammonia and hydrogen peroxide, which was detected in an electrochemical flow-through cell at +650 mV vs. Pt/(0.1 M KCl). The detection limit of alpha-ketoglutarate in the coupled packed bed reactors was 1 microM (defined as 3 S/N), the linear range 0-100 microM, and the sensitivity 0.80 nA/microM (R(2) 0.99). In the coupled expanded bed reactors, the detection limit of alpha-ketoglutarate was 7 microM (defined as 3 S/N), the linear range and the sensitivity being 0-500 microM and 0.11 nA/microM (R(2) 1.00), respectively. The response time (defined as the time between peak rise and return to baseline) was 5 min for coupled packed beds (injection of supernatant), and 12 min for coupled expanded beds (injection of sample containing cellular and particulate matter). Several other parameters, such as reactor stability, flow rate dependency, bed expansion, glutamate interference, etc. were investigated and characterised. When analysing real samples from a fermentation broth, the same results were obtained independent of the nature of the reactor system (packed or expanded bed). The hereby described system can easily be automatised and controlled from a personal computer.

Investigations into biochemical changes due to diurnal variation and estrus cycle in female rats using high-resolution (1)H NMR spectroscopy of urine and pattern recognition

Metabonomic methods utilizing (1)H NMR spectroscopy and pattern recognition analysis (NMR-PR) have been applied to investigate biochemical variation in a control population of female rats over time in relation to diurnal and estrus cycle fluctuations. Urine samples were collected twice daily (6 AM-6 PM and 6 PM-6 AM) from female rats (n = 10) for a period of 10 days. (1)H NMR spectroscopic analysis and PR were performed on each sample. Subtle differences in the endogenous metabolite excretion profiles of urine samples at the various stages of the estrus cycle were observed. The main inherent metabolic clustering in the principal components analysis (PCA) maps was related to interrat variation and was observed in the first two principal components (PCs), accounting for 66% of the variance in these data. Separation of urinary data according to time of sampling (day and night) was achieved in the lower PCs. Some of the differences in the urinary profiles of day and night samples causing this separation were attributed to the increase in metabolic activity of the rat during the night. Individual rat data were also mapped as a function of time, using PCA, to produce a metabolic trajectory, which in a number of cases facilitated separation of one or more stages of the estrus cycle. Several of the fluctuations observed between urine samples collected during the different stages of the estrus cycle may be related to hormone levels. Although variation in metabolite profiles relating to both diurnal and hormonal variation could be detected these perturbations were minor compared with the effects observed due to interrat variation. This is the first time that a hormonal cycle has been described for individuals based on NMR spectroscopic and multivariate analysis of metabolic data and shows the value of metabonomic methods in the investigation of physiological variation and rhythms.

Inhibitory effect of KW-3902, an adenosine A(1) receptor antagonist, on p-aminohippurate transport in OK cells

KW-3902 (8-(noradamantan-3-yl)-1,3-dipropylxanthine) is a novel potent and selective adenosine A(1) receptor antagonist. We examined the effect of KW-3902 on p-aminohippurate (PAH) transport in opossum kidney (OK) epithelial cells. Pretreatment for 3 h with KW-3902 inhibited the transcellular transport of PAH across OK cell monolayers from the basal to the apical side. The uptake of PAH across the basolateral membrane of OK cells was inhibited by KW-3902 pretreatment in a time- and concentration-dependent manner. A kinetic analysis revealed that the inhibitory effect of KW-3902 on the basolateral PAH uptake was due to an increase in the Michaelis constant (K(m)) as well as a decrease in the maximum uptake rate (V(max)), showing that the inhibition was a mixed type. Pretreatment with adenosine deaminase or 8-cyclopentyl-1,3-dipropylxanthine, another selective adenosine A(1) receptor antagonist, also decreased the basolateral PAH uptake. KW-3902 pretreatment had no effect on the concentration of intracellular alpha-ketoglutarate which exchanges for PAH across the basolateral membrane of OK cells. These results suggest that KW-3902 has an inhibitory effect on PAH transport in OK epithelial cells.

Ornithine-alpha-ketoglutarate (OKG) supplementation is more effective than its component salts in traumatized rats

Addition of an anabolic stimulus during nutritional support seems to be a reasonable adjunct to augment protein synthesis. Ornithine-alpha-ketoglutarate (OKG) has been used for this purpose in many pathological situations, but the mechanism of action is poorly understood. We have evaluated the relative metabolic efficacy of four isonitrogenous diets with or without the addition of alpha-ketoglutarate (alpha KG) or ornithine (ORN), in a rat trauma (bilateral femur fracture) model. Both control and traumatized rats were starved for 2 d. Then for 4 d, the control rats were pair-fed to the traumatized rats, one of the four isonitrogenous diets: the basal diet was a casein-based liquid diet; the ORN and OKG diets were the basal diet in which 10% of the dietary nitrogen was replaced by ORN- or OKG-nitrogen, respectively; the alpha KG diet contained equivalent amounts of alpha KG as were present in the OKG diet. Body weight gain per gram of nitrogen intake was similar in all four diet groups of both control and traumatized rats. The fraction of nitrogen intake that was retained in the body was significantly higher in OKG-fed traumatized rats (23%) than in the corresponding basal diet-fed rats. Plasma and muscle free amino acid concentrations were comparable in OKG- and ORN-fed rats but not in OKG- and alpha KG-fed rats. Our data suggest that the mechanism of OKG action may be associated with increases in growth hormone and insulin, as well as the production of metabolites of ORN and alpha KG. OKG has better metabolic benefits than its two components given separately in the nutritional support of injured rats.

Luminometric measurement of subnanomole amounts of key metabolites in extracts from isolated heart muscle cells

In principle, luminometry allows very sensitive metabolite measurements as shown with standards in aqueous solutions (e.g., buffers). However, components of complex biological samples may largely interfere with luminometric reactions. We now describe a procedure by which subnanomole amounts of intermediary metabolites (malate, glucose 6-phosphate) can be measured by luminometry in extracts from isolated mammalian cells, namely rat heart muscle cells. Basically, measurements occur in two steps: (i) Enzymatically catalyzed reactions involving the metabolite to be measured lead to the stoichiometric production of NAD(P)H; (ii) the oxidation of this NAD(P)H in a luciferase/reductase system results in light production which is proportional to the original concentration of the metabolite. The reaction scheme is thus as follows: (1) Metabolite (malate, glucose 6-phosphate) + NAD(P)+ --> X + NAD(P)H + H+; (2) NAD(P)H + O2 + RCOH --> NAD(P)+ + RCOOH + H2O + hnu. The cardiomyocytes used are previously subjected to an ethanolic extraction in which the cellular NAD(P)H is destroyed by acidification. Subsequent evaporation of the extracts allows to neutralize and to concentrate the samples. This contributes, along with other experimental maneuvers, to increasing the sensitivity of the method. With this procedure, we were able to detect amounts of approximately 70 pmol of malate and approximately 90 pmol of glucose 6-phosphate in cardiomyocyte samples. In addition, the calculated cellular concentrations of malate and glucose 6-phosphate (101.1 +/- 4.5, and 202.8 +/- 26.1 microM, respectively, in the absence of exogenous substrate) correspond to values previously reported for heart tissue. In principle, the procedure described could be applied to the measurement of any ethanol-extractable metabolite that can be converted in reactions involving NAD(P)+.

alpha-Ketoglutarate assay based on fluorescence quenching by NADH

A new assay procedure for the measurement of ketoglutarate concentrations is described which is based on substrate-induced quenching (SIQ) of a fluorophore. The method makes use of the photoreaction between a fluorophore (thionine) and NADH. The latter is consumed during an enzymatic reaction between ketoglutarate and L-glutamic dehydrogenase. The conversion yield of cofactor from its reduced form to oxidized forms represented as an overall change in the population of the excited state population of the fluorophore thionine. An empirical relation is described that correlates initial substrate concentration to the observed yield of the cofactor conversion via a fluorescence recovery constant,Kt. The analysis of data obtained over a range of 0-500 microM results in a constant of 2748 M-1. The applicability of the proposed method is demonstrated by performing the assay for alpha-ketoglutarate in human urine. The ketoglutarate SIQ assay was not affected by the background interference that is inherent to this complex matrix.

Multiplet structure of 13C NMR signal from glutamate and direct detection of tricarboxylic acid (TCA) cycle intermediates

For the first time, 13C NMR signals are shown from 13C-enriched, low-level tricarboxylic acid (TCA) cycle intermediates from extracts of normal cardiac tissue. As the low tissue content of the key intermediates alpha-ketoglutarate (alpha-KG) and succinate (SUC) in normal, well perfused tissues has until now precluded direct NMR detection from intact tissues and tissue extracts, 13C NMR signal from glutamate has generally been used to infer the isotopomer patterns of intermediates that are in chemical exchange with glutamate. However, the required assumptions regarding intracellular compartmentation for such indirect analysis have not been previously tested, as glutamate is largely cytosolic while the TCA cycle enzymes are located in the mitochondria. Chromatographic isolation of alpha-KG and SUC from heart tissue extracts allowed isotopomer analysis to be performed for comparison with that of glutamate. At steady state, a direct relationship between glutamate and alpha-ketoglutarate isotopomers was found, but succinate isotopomers matched those of glutamate only in hearts that displayed negligible contributions from the oxidation of unlabeled endogenous carbon sources.

Assay of blood and tissue oxaloacetate and alpha-ketoglutarate by isotope dilution gas chromatography-mass spectrometry

The assay of oxaloacetate and alpha-ketoglutarate in biological samples is complicated by their chemical instability and low concentrations. We present a quantitative assay for physiological concentrations of these metabolites by isotope dilution gas chromatography-mass spectrometry. Samples are spiked with the corresponding internal standards of [U-13C4]oxaloacetate and [U-13C5] alpha-ketoglutarate prior to their treatment with hydroxylamine. After ethyl acetate extraction and evaporation of the organic phases, the oximes are converted to t-butyldimethylsilyl ethers and analyzed by selected ion monitoring gas chromatography-mass spectrometry of the [M-57]+ ion in electron impact. Although the internal standards of [U-13C4]oxaloacetate and [U-13C5] alpha-ketoglutarate are not commercially available, they can easily be synthesized in 30 min by reacting [1,2,3,6-13C4]citrate with citrate lyase, and L-[U-13C5]glutamate with pyruvate and glutamate-pyruvate transaminase, respectively. Because of their chemical instability, the internal standards are prepared on the day of the analysis. A stock solution of [1,2,3,6-13C4]citrate is prepared from L-[U-13C4]aspartate using citrate synthase and glutamate-oxaloacetate transaminase and then purified and kept frozen until required. The detection limit of the method is 0.05 nmol in a given sample. The method was applied to measurements of oxaloacetate and alpha-ketoglutarate in human blood and rat liver.

Fast method for the simultaneous determination of 2-oxo acids in biological fluids by high-performance liquid chromatography

A fast and sensitive method for the single-run quantification of various 2-oxo acids including 2-ketoglutarate, glyoxylate and pyruvate is described. It ensures good separation of peaks with minor interference by other substances. The 2-oxo acid derivatives are measured photometrically at 324 nm after derivatization with phenylhydrazine and subsequent isocratic separation with ethanolic phosphate buffer on a C18 reversed-phase HPLC column. Recovery was found to be complete [range: 96.3 +/- 5.6% (pyruvate) to 104.8 +/- 5.2% (2-ketoglutarate)]. Detection limits ranged from less than 0.1 mumol/l (glyoxylate) to 0.25 mumol/l (2-ketoglutarate and pyruvate). Results for all substances examined showed good linearity with correlations (r2) of equal to or better than 0.998.

Quantitative analysis of 2-oxoglutarate in biological samples using liquid chromatography with electrochemical detection

This paper describes a technique for quantitative analysis of 2-oxoglutarate (alpha-ketoglutarate) in biological samples using liquid chromatography with electrochemical detection (LC-EC). This method utilizes a simplified, efficient sample preparation designed to select for 2-oxoglutarate and similar compounds by derivatization with phenylhydrazine. The response was linear over the range from 62.5 to 1000 ng/ml. The least quantifiable concentration was 62.5 ng/ml and the least detectable concentration was 25 ng/ml. To test the ability of the assay to measure 2-oxoglutarate in biological samples, this method was used to quantitate the 2-oxoglutarate content in chick osteoblast cultures and to determine the ability of the assay to accurately measure a standard addition of 500 ng/ml 2-oxoglutarate when added to a sample of the forementioned groups. The 2-oxoglutarate content of these cells was 6.67 +/- 1.20 ng/micrograms DNA or 105 +/- 18 ng/cell layer (mean +/- 95% confidence interval) and the assay accurately measured the standard addition. This method was also used to quantitate 2-oxoglutarate content in whole embryonic chick calvariae containing 6.40 +/- 0.95 ng/mg dry bone weight or 37.5 +/- 5.5 ng/bone. This assay provides significantly lower detection limits than the currently available procedures and is suitable for determination of 2-oxoglutarate in biological samples where very low amounts of 2-oxoglutarate are found. This method is the first application of LC-EC for quantitating 2-oxoglutarate.

Effect of fluoxetine on rat liver mitochondria

The in vitro and in vivo effects of fluoxetine (and its active metabolite norfluoxetine) on mitochondrial respiration and F0F1-ATPase were studied, respectively, in mitochondria and submitochondrial particles isolated from rat liver. Fluoxetine in vitro inhibited state 3 mitochondrial respiration for alpha-ketoglutarate and succinate oxidations (50% of effect at 0.25 and 0.35 mM drug concentrations, respectively); stimulated state 4 for succinate; and induced a decrease in the respiratory control ratio (RCR) for both oxidizable substrates. The F0F1-ATPase activity was determined at various pH levels in the absence and presence of Triton X-100. The solubilized form was not affected markedly, but an inhibition, apparently non-competitive, was observed for the membrane-bound enzyme, with 50% of the effect at a 0.06 mM drug concentration in pH 7.4. These results suggest that fluoxetine in vitro acts on F0F1-ATPase through direct interaction with the membrane F0 component (similar to oligomycin), or first with mitochondrial membrane and then affecting F0. A very similar behavior concerning the respiratory parameters and F0F1-ATPase properties was observed with norfluoxetine. The in vivo studies with fluoxetine showed stimulation of mitochondrial respiration in state 4 for alpha-ketoglutarate or succinate oxidations in acute or prolonged treatments (1 hr after a single i.p. dose of 20 mg of drug/kg of body weight, and 22 hr after 12 days of treatment with a daily dose of 10 mg/kg of body weight, respectively), indicating uncoupling of oxidative phosphorylation. Pronounced changes were not observed in the K0.5 values of F0F1-ATPase catalytic sites, but the Vmax decreased during the prolonged treatment. The results show that fluoxetine (as well as norfluoxetine) has multiple effects on the energy metabolism of rat liver mitochondria, being potentially toxic in high doses. The drug effects seem to be a consequence of the drug and/or metabolite solubilization in the inner membrane of the mitochondria.

Effect of L-carnitine on cerebral and hepatic energy metabolites in congenitally hyperammonemic sparse-fur mice and its role during benzoate therapy

Sparse-fur (spf) mutant mice with X-linked ornithine transcarbamylase deficiency were used to study the effect of L-carnitine on energy metabolites in congenital hyperammonemia. L-Carnitine was used at doses of 2, 4, 8, or 16 mmol/kg body weight (BW), and levels of ammonia, glutamine, glutamate, and some intermediates of energy metabolism were measured in brain and liver of spf/Y mice. Cerebral and hepatic levels of ammonia were decreased with 4 mmol L-carnitine (P < .001), whereas other doses did not seem to have any effect on this metabolite. Cerebral levels of glutamine were decreased following administration of L-carnitine at doses of up to 4 mmol/kg BW, whereas hepatic glutamine levels remained unaltered at all doses of L-carnitine. Both cerebral and hepatic levels of pyruvate, lactate, and alpha-ketoglutarate were decreased at doses of up to 8 mmol L-carnitine/kg BW. L-Carnitine treatment elevated adenosine triphosphate (ATP), free coenzyme A (CoA), and acetyl CoA levels in both brain and liver of spf/Y mice. Cytosolic and mitochondrial redox ratios of spf/Y mice, which were altered by congenital chronic hyperammonemia, were partially corrected by L-carnitine administration. L-Carnitine supplementation to spf/Y mice during sodium benzoate therapy also restored the availability of free CoA and ATP, thus counteracting the adverse effects of higher doses of sodium benzoate. These changes in free CoA and acetyl CoA levels could be due to the deinhibition of pantothenate kinase and stimulation of fatty acid oxidation by L-carnitine.(ABSTRACT TRUNCATED AT 250 WORDS)

Nitrogen regulation in an Escherichia coli strain with a temperature sensitive glutamyl-tRNA synthetase

Escherichia coli cells carrying the gltX351 allele are unable to grow at 42 degrees C (Ts phenotype) due to an altered glutamyl-tRNA synthetase. We found that gltX351 cells display a new phenotype termed Gsd-, i.e. an inability to raise glutamine synthetase activity above low constitutive levels in minimal medium with 6.8 mM glutamine as sole nitrogen source. When 0.5 mM NH4+ or 12 mM glutamate replaced glutamine, the glutamine synthetase activities of gltX351 cells were raised to wild-type levels. Northern experiments showed that the Gsd- phenotype is the result of an impairment in transcription initiation from the Ntr-regulated promoter, glnAp2. Intragenic and extragenic secondary mutations appeared frequently in gltX351 cells, which suppressed their Gsd- but not their Ts phenotype. Moreover, in heterozygous gltX+/gltX351 partial diploids, gltX351 was dominant for the Gsd- phenotype and recessive for the Tr phenotype. A slight increase in the glutamine pool and in the intracellular glutamine: 2-oxoglutarate ratio was also observed but this could not account for the Gsd- phenotype of gltX351 cells. In cells carrying gltX351 and a suppressor of the Gsd- phenotype, sup-1, tightly linked to gltX351, the glutamine pool and glutamine: 2-oxoglutarate intracellular ratio were even higher than in the gltX351 single mutant. These results indicate that the gltX351 mutant polypeptide may be the direct cause of the Gsd- phenotype. The possibility that it interacts with one or more components that trigger the Ntr response is discussed.

Flow-injection analysis of amino acids and their metabolites by immobilized vitamin B6-dependent enzymes. Sensitive determination of L-aspartate, L-glutamate, 2-oxoglutarate, and oxaloacetate

Sensitive flow-injection analyses of aspartate, glutamate, 2-oxoglutarate, and oxaloacetate were developed. The analytes were enzymatically coupled with NADH which was monitored by light emission from immobilized bacterial bioluminescence enzymes. Aspartate (or oxaloacetate) was assayed on the basis of NADH consumption by introducing the sample through a coimmobilized aspartate aminotransferase-malate dehydrogenase column. The assay responded linearly from 100 pmoles to 5 nmoles per assay. Glutamate (2-oxoglutarate) was determined by formation of NADH in the glutamate dehydrogenase reaction. The measuring range for glutamate was from 10 pmoles to 100 nmoles per assay. The precision of the flow-injection method was generally excellent, and the sensitivities of the described assays were 100-1000-fold higher than with spectrophotometric methods. The immobilized enzyme preparations were stable for several months in storage, and the enzyme columns could be used for 600-800 analyses. Flow-injection analyses of amino acids and related compounds by NADH/bioluminescence-coupled reactions provide a sensitive, fast, and inexpensive assay method for a wide variety of purposes.

The onset of mammary secretion of medium-chain-length triglyceride fatty acids in the cow milked pre-partum

Six Friesian cows were milked daily, and arterial and mammary venous blood samples were taken between day 266 of gestation and day 6 after parturition. Samples of blood plasma were analysed for their content of acetate and progesterone, and mammary secretion for potassium, isocitrate, 2-oxoglutarate and triglyceride fatty acids. The onset of secretion of medium-chain triglyceride fatty acids was preceded by, or coincided with, increases of potassium and isocitrate concentration in the secretion. The onset of fatty acid secretion was not accompanied by any change in the gland's extraction of acetate from the circulation, and did not occur at a consistent time relative to parturition or changes in plasma progesterone concentration.

A spectrophotometric procedure for measuring oxoglutarate and determining aminotransferase activities using nicotinamide adenine dinucleotide phosphate-linked glutamate dehydrogenase from algae

A new spectrophotometric procedure is described for determining glutamate-dependent activities of aspartate aminotransferase, alanine aminotransferase, and ornithine aminotransferase with NADPH-linked glutamate dehydrogenase (GDH) from nitrate-grown Stichococcus bacillaris. The algal NADPH-GDH is highly specific for oxoglutarate and can catalyze the reduction of this keto acid in the presence of high glutamate concentrations, and thus is suitable for the measurement of oxoglutarate produced in glutamate-dependent amino-transferase reactions. The alga produces large amounts of NADPH-GDH which can be adequately purified in a few simple steps. The purified enzyme can be stored at 4 degrees C for several weeks without any detectable loss of activity. The algal NADPH-GDH can also be used for the estimation of small amounts of oxoglutarate in aqueous extracts.

Assay of prolyl 4-hydroxylase by the chromatographic determination of [14C]succinic acid on ion-exchange minicolumns

An assay for prolyl 4-hydroxylase (EC 1.14.11.2) is described which measures succinic acid produced during the decarboxylation of 2-oxoglutaric acid in the presence of poly(L-Pro-Gly-L-Pro). [1-14C]Succinic acid was separated from its precursor 2-oxo[5-14C]glutaric acid by using ion-exchange minicolumns. The contamination of succinic acid by 2-oxoglutaric acid was approx. 1%, and the recovery of succinic acid was 100%. Kinetic parameters of prolyl 4-hydroxylase measured by the assay showed good agreement with published values. Our experience indicates that the measurement of prolyl 4-hydroxylase by the production of succinic acid is especially suited to investigations involving large numbers of assays.

Comparisons of 17 lots of 2-oxoglutarate, and specifications for use of this substrate in reference methods

We examined 17 lots of 2-oxoglutarate (seven acid forms, three K salt forms, and seven Na salt forms), obtained from eight commercial suppliers, for suitability for measuring aspartate aminotransferase (EC 2.6.1.1) and alanine aminotransferase (EC 2.6.1.2) in human serum. Measurements of the catalytic activity concentrations of these two aminotransferases with each of these 17 preparations were not sufficiently sensitive to distinguish good from poor-quality material. Thus, we ranked these lots for purity, by specific analysis with glutamate dehydrogenase and by liquid chromatography, and determined the water content, acid content, and spectral characteristics of each. On the basis of a 2-oxoglutarate assay value by glutamate dehydrogenase of 98% or greater, we considered seven of the preparations acceptable and 10 unacceptable. The molar absorptivities (L X mol-1 X cm-1, mean +/- SD) of the seven acceptable lots in 1 mol/L HCl were: epsilon 325 nm = 9.12 +/- 0.02 (CV = 0.2%), epsilon 279 nm = 2.63 +/- 0.23 (CV = 9.9%), and epsilon 245 nm = 37.9 +/- 4.1 (CV = 10.9%). Use of these spectrophotometric limits alone unambiguously distinguished the inferior lots of 2-oxoglutarate. We urge the inclusion of detailed spectrophotometric specifications for 2-oxoglutarate in Reference Methods for aminotransferase measurements.

Nylon tube-immobilized creatinine iminohydrolase and glutamate dehydrogenase in serum and urine creatinine analysis

Immobilized enzyme nylon-tube reactors incorporating creatinine iminohyrolase (CI) and glutamate dehydrogenase (GDH) were used to assay creatinine in serum and urine. Optimum substrate concentrations for the assay were determined. The reactors were incorporated into a continuous flow system for creatinine analysis. The method was evaluated with respect to linearity, sample interaction, precision, accuracy, and analytical recovery. Comparison studies were carried out with a standard Jaffé method and the effect of interfering substances was investigated. From the results obtained, it was concluded that the assay was suitable as a simple, reliable, and specific method for serum and urine creatinine determinations.

Microdetermination of 2-ketoglutaric acid in plasma and cerebrospinal fluid by capillary gas chromatography mass spectrometry; application to pediatrics

Quantification of 2-ketoglutaric acid in plasma and cerebrospinal fluid as its O-trimethylsilyl++-quinoxalinol derivative by gas chromatography chemical ionization mass spectrometry is described with benzoylformic acid as internal standard. This technique, with ammonia as reactant gas, only detects the protonated molecular ions. The recovery of 2-ketoglutarate from perchloric-deproteinized plasma is 99.7 +/- 1.2%. The normal value of 2-ketoglutarate in children is 8.6 +/- 2.6 mumol l-1 (mean +/- standard deviation) in plasma (n = 25) and 4.8 +/- 1.4 mumol l-1 in cerebrospinal fluid (n = 20). The plasma level of 2-ketoglutarate is correlated with urea concentration (r = 0.96; p less than 0.001) in healthy subjects and in patients with chronic renal insufficiency. Increased values are found in one case of pyruvate carboxylase deficiency, and inconstantly in diabetes; physiological variations are described during fasting and after an oral glucose load.

High-performance liquid chromatography of alpha-keto acids in human saliva

alpha-Keto acids in human mixed saliva collected without stimulation were analysed by reversed-phase ion-pair high-performance liquid chromatography (HPLC). Several alpha-keto acids were found in saliva and their concentrations were: alpha-ketoglutaric acid (KGA), 221 +/- 142; pyruvic acid (PA), 7490 +/- 5600; alpha-ketoisovaleric acid (KIVA), 61 +/- 23; alpha-ketoisocaproic acid (KICA), 137 +/- 79; alpha-keto-beta-methylvaleric acid (KMVA), 41 +/- 19 nmol/dl (mean +/- SD, n = 40). Their levels proved to be lower than those in plasma, except that of PA. Their concentrations in saliva showed individual variation compared with those in blood.

Enzymic determination of branched-chain amino acids

Transamination of branched-chain amino acids to (alpha-oxoglutarate, catalyzed by leucine aminotransferase coupled to the glutamate dehydrogenase reaction, is used in an enzymic assay for determination of branched-chain amino acids in serum and tissue homogenates. The coefficients of variation of the method within-day and day-to-day are 2.4 and 6.5%, respectively. Analytical recovery of physiological concentrations of branched-chain amino acids added to serum is near 100%. Measurements in serum of healthy subjects revealed normal values similar to those found by use of other methods. During prolonged fasting the concentration of these amino acids in serum first increases, reaching a maximum by three days, followed by a successive decline.

Thiamine deficiency and glyoxylic acid

The effect of thiamine deficiency on glyoxylic acid metabolism in mice and rats was investigated to determine whether the vitamin deficiency results in gross effects on glyoxylate levels via an alteration in the activity of alpha-ketoglutarate:glyoxylate carboligase. Thiamine-deprived or pyrithiamine-treated mice did not show a decreased oxidation of [1-14C]glyoxylate to respiratory CO2; there was some decrease in the conversion of [2-14C]glyoxylate into CO2 by pyrithiamine-treated mice, but not by thiamine-deprived animals. Dietary thiamine deprivation caused a decrease in carboligase levels in liver but no effect on levels in three brain regions. Pyrithiamine treatment had no significant effect on liver carboligase activities, but did decrease the levels in cerebrum, cerebellum and brainstem. Thiamine-deprived and pyrithiamine-treated mice showed decreased urinary glycolic acid excretion Glyoxylic acid excretion by thiamine-deprived rats was monitored in order to re-examine a previous report by another laboratory that glyoxyluria occurs under these conditions. Trace amounts of glyoxylate could be detected in the urine of rats fed thiamine-deficient diet for 3-5 weeks, but urinary glyoxylate was not detectable at later stages of thiamine deprivation. These results do not support a significant role for alpha-ketoglutarate:carboligase activity in the primary etiology of thiamine deficiency syndromes.

Tumor host relations. VI. Is alpha-ketoglutarate a tumor marker? Association with tumor extent in humans--correlation with tumor size in rats

A 4-year survey is presented on the alpha-ketoglutarate (KG) values in whole blood of 200 patients with malignant neoplasms mainly of the gastrointestinal tract and the female breast. A group of patients with benign surgical diseases served as control. KG showed an association with the extent of the primary tumor classified according to the TNM-scheme. The percentages of single values above the 2s-range of the control were as follows: T2: 18%,T3: 41%, and T4: 64%. The mean value of KG had highly significantly increased already in stage T2 as compared to the control group. Rats bearing the Yoshida sarcoma showed a significant correlation between the tumor size and the daily excretion of KG into urine during the early stage of tumor growth. The results suggested that KG cannot be regarded as an early tumor marker in humans, but may be of some value as an aid for the differential diagnosis in advanced tumor stages.

Subcellular distribution of di- and tricarboxylates and pH gradients in perfused rat liver

The subcellular distribution of malate, 2-oxoglutarate, citrate, aspartate and glutamate and the mitochondrial and cytosolic pH values were determined in perfused livers from fed and fasted rats. The method of fractionation of the freeze-dried tissue in non-aqueous solvents was employed. The following results were obtained: 1) Di- and tricarboxylates are not equally distributed between mitochondria and cytosol. Under the two metabolic conditions studied, the concentrations of citrate and 2-oxoglutarate are higher and those of glutamate and aspartate are lower in the mitochondria than in the cytosol. The distribution of malate varies with the metabolic state. 2) From the distribution of 5,5-dimethyl-2,4-oxazolidinedione it was calculated that the mitochondrial matrix has a more alkaline milieu than the cytosol. The cytosol is also more acidic than the perfusate. The pH difference between mitochondria and cytosol is 0.3 in the fed state and 0.6 in the fasted one, whereas the pH difference between perfusate and cytosol is 0.4 in the fed state and 0.2 in the fasted one. 3) In livers from fed rats, citrate, malate and 2-oxoglutarate appear to be distributed according to the pH gradient across the mitochondrial membrane, whereas in the fasted state, the distribution does not correspond to the pH gradient. Glutamate and aspartate do not follow the pH gradient in either metabolic state. 4) The data indicate that the pH gradient across the mitochondrial membrane does not reflect the membrane potential or the energy state of mitochondria in the intact cell.

Distribution of metabolites between the cytosolic and mitochondrial compartments of hepatocytes isolated from fed rats

In isolated hepatocytes from normal fed rats, the subcellular distribution of malate, citrate, 2-oxoglutarate, glutamate, aspartate, oxaloacetate, acetyl-CoA and CoASH has been determined by a modified digitonin method. Incubation with various substrates (lactate, pyruvate, alanine, oleate, oleate plus lactate, ethanol and aspartate) markedly changed the total cellular amounts of metabolites, but their distribution between the cytosolic and mitochondrial compartments was kept fairly constant. In the presence of lactate, pyruvate or alanine, about 90% of cellular aspartate, malate and oxaloacetate, and 50% of citrate was located in the cytosol. The changes in acetyl-CoA in the cytosol were opposite to those in the mitochondrial space, the sum of both remaining nearly constant. The mitochondrial acetyl-CoA/CoASH ratio ranged from 0.3-0.9 and was positively correlated with the rate of ketone body formation. The mitochondrial/cytosolic (m/c) concentration gradients for malate, citrate, 2-oxoglutarate, glutamate, aspartate, oxaloacetate, acetyl-CoA and CoASH averaged from hepatocytes under different substrate conditions were determined to be 1.0, 8.8, 1.6, 2.2, 0.5, 0.7, 13 and 40, respectively. From the distribution of citrate, a pH difference of 0.3 across the inner mitochondrial membrane was calculated, yet lower values resulted from the m/c gradients of 2-oxoglutarate, glutamate and malate. The mass action ratios for citrate synthase and mitochondrial aspartate aminotransferase have been calculated from the metabolite concentrations measured in the mitochondrial pellet fraction. A comparison with the respective equilibrium constants indicates that in intact hepatocytes, neither enzyme maintains its reactants at equilibrium. On the assumption that mitochondrial malate dehydrogenase and 3-hydroxybutyrate dehydrogenase operate near equilibrium, the concentration of free oxaloacetate appears to be 0.3-2 micron, depending on the substrate used. Plotting the calculated free mitochondrial oxaloacetate concentration against the citrate concentration measured in the mitochondrial pellet yielded a hyperbolic saturation curve, from which an apparent Km of citrate synthase for oxaloacetate in the intact cells of 2 micron can be derived, which is comparable to the value determined with purified rat liver citrate synthase. The results are discussed with respect to the supply of substrates and effectors of anion carriers and of key enzymes of the tricarboxylic acid cycle and fatty acid biosynthesis.

The effects of vitamin D on the rat kidney metabolism under conditions of experimental hypercalcemia

The effects of vitamin D3 on rat kideney metabolism under conditions of experimental hypercalcemia. Acta Physiol. Pol., 1978, 29 (2) 153--159. The effect of vitamin D3 on renal gluconeogenesis processes was studied in the rat. The performed estimations of gluconeogenesis rate from malate and lactate demonstrated significant increases of glucose formation rate when kidney cortex slices of the vitamin D3 treated animals were analyzed. Further studies on the mechanism of the observed phenomenon were performed using kidney cell fractionation procedure and fluorometric estimation of the concentration of selected gluconeogenetic metabolites. Significant increases of phosphoenolpyruvate concentration in the cytosol fraction and citrate concentration in the mitochondrial fraction were observed. Comparison of the described action of vitamin D3 on gluconeogenesis and the effect of parathyriod hormone, as known from the literature suggests similar mechanism of both factor actions. A possibility of vitamin D3 action through the increase in intracellular calcium has been discussed.

[Genetically determined variability in rat behavior and its biochemical correlates]

Using the combination of extremely high and low values of two independent behavioural variables (activity and frequency of defecation in open field) four groups of rats were selected with different CNS reactivity corresponding to the types of higher nervous activity described by I.P. Pavlov. These groups of rats revealed significant differences in reactivity to stress and drugs, in social behaviour and biochemical pattern. They may represent a useful tool for the research in experimental psychology, neurophysiology, psychopharmacology and other branches of science.

Determination of pools of tricarboxylic acid cycle and related acids in bacteria

Methods for sampling, extracting, and quantitating the metabolic pools of organic acids from bacteria have been developed. The concentration of these metabolites was determined by a new gas chromatographic method that can quantitatively determine the levels of lactate, pyruvate, fumarate, succinate, malate, alpha-ketoglutarate, and citrate. Values obtained were confirmed by fluorimetric analyses of five of the individual acids. In Escherichia coli, pools range from about 1 to 5 mumol/g of dry weight, with a variation in replicate samples of 5 to 15%. Under similar conditions, these pools in Bacillus licheniformis are in the same range, although the pyruvic acid pool is significantly larger.