Determination of pyridine and adenine nucleotide metabolites in Bacillus subtilis cell extract by sweeping borate complexation capillary electrophoresis

Methanol plug assisted sweeping-micellar electrokinetic chromatography for the determination of dopamine in urine by violet light emitting diode-induced fluorescence detection

The use and limitations of a methanol plug assisted sweeping-micellar electrokinetic chromatography (sweeping-MEKC) method is described. Using naphthalene-2,3-dicarboxaldehyde (NDA)-labeled dopamine as a model compound, this new method was also used in the determination of dopamine in actual urine samples. An inexpensive violet light emitting diode (LED) was used for the light source, because this is suitable for fluorescence excitation. The number of theoretical plates of the analyte was determined to be approximately 1 x 10(5) and approximately 2 x 10(5) by means of MEKC and sweeping-MEKC and this was improved to approximately 1 x 10(6) when the methanol plug assisted mode was applied. In addition, the detection limit of NDA-labeled dopamine was determined to be 9.1 x 10(-7) and 1.2 x 10(-8)M by means of MEKC and sweeping-MEKC and this was improved to 4.7 x 10(-9)M when the methanol plug assisted sweeping-MEKC mode was applied.

Tracking variations in nicotinamide cofactors extracted from cultured cells using capillary electrophoresis with multiphoton excitation of fluorescence

Nicotinamide cofactors play numerous roles in cellular metabolic and biosynthetic reactions and intracellular signaling events. Recently, nicotinamide cofactors have been implicated in the function of cellular biological clocks. To gain insight into the possible roles of nicotinamide cofactors in complex time-related events, we have developed a rapid and sensitive method for extraction of NAD(P)(H) from cultured cells, separation of analytes by capillary electrophoresis, and detection by multiphoton excitation of fluorescence. Extraction and quantitation steps have been systematically characterized for optimal pH, detergent, temperature, sonication, filtration, efficiency, accuracy, and reproducibility. The method is suitable for extractions at 2- to 3-h intervals over 1 day or more or as frequently as every hour for shorter durations. Natively fluorescent NAD(P)H are assayed directly, and nonfluorescent NAD(P) are enzymatically reduced to their fluorescent counterparts before analysis. The method yields accurate values for cellular NADP, NADPH, and total NAD(H) levels and relative information on cellular NADH concentration; modification of the procedure allows full quantitation of all relevant species. We conclude that these assays are more suitable than any yet published for tracking variations in nicotinamide cofactor levels over periods of 1 day or more.

Simultaneous determination of the main metabolites in rice leaves using capillary electrophoresis mass spectrometry and capillary electrophoresis diode array detection

The study of the metabolomics of primary metabolites using conventional chemical analyses requires a high-throughput method. Chemical derivatizations are a prerequisite for gas-chromatographic separation, and a large sample quantity is needed for liquid-chromatographic separation and nuclear magnetic resonance detection systems. Recently, we have developed a capillary electrophoresis-mass spectrometry (CE-MS) technology that can simultaneously quantify a large number of primary metabolites, using only a small quantity of samples, and without any chemical derivatizations. Parallel use of a capillary electrophoresis-diode array detector (CE-DAD) system further enables almost all water-soluble intracellular metabolites to be analyzed. We demonstrate, with rice leaves, a simple and rapid method of sample preparation for CE analysis; using this method, we have successfully measured the levels of 88 main metabolites involved in glycolysis, the tricarboxylic acid cycle, the pentose phosphate pathway, photorespiration, and amino acid biosynthesis.

Two-Dimensional Separation Method for Analysis of Bacillus subtilis Metabolites via Hyphenation of Micro-Liquid Chromatography and Capillary Electrophoresis

A novel two-dimensional separation method, which hyphenated chromatography and electrophoresis, was developed for analysis of Bacillus subtilis metabolites. Micro-liquid chromatography (LC) with a monolithic silica-ODS column was used as the first dimension, from which the effluent fractions were further analyzed by capillary electrophoresis (CE) acting as the second dimension. Concentration strategies, namely, dynamic pH junction and sweeping, were selectively employed to interface the two dimensions, which proved to be beneficial for the detection of metabolites. For system evaluation, an artificial sample containing 54 standard metabolites was separated according to their hydrophobicity by micro-LC with gradient mode. The early-eluting fractions were separated by capillary zone electrophoresis in combination with dynamic pH junction, while the late-eluting fractions were separated by sweeping micellar electrokinetic chromatography. The middle fractions were analyzed by both modes of CE. Under the optimum conditions, all the components in the artificial sample could be well resolved. The method was applied to profile B. subtilis metabolites. Some crucial metabolites were identified. This method provided great potential for resolving complex biological samples containing compounds having different characteristics.

On-line sample preconcentration of cationic analytes by dynamic pH junction in capillary electrophoresis

To improve detection sensitivity of cationic analytes, a dynamic pH junction technique was examined. Dynamic pH junction is an on-line focusing method in capillary electrophoresis (CE) based on the difference in the analyte's mobility between the background electrolyte (BGE) and sample matrix. The effects of pH values and concentrations of the BGE and the sample matrix on dynamic pH junction were examined. Optimization of analyte focusing resulted in enhanced detection responses of about 100-160-fold in terms of peak heights for some anilines in comparison to conventional injections. In particular, the concentration limits of detection (LOD) (S/N = 3) for the test anilines obtained with dynamic pH junction were from 1.9 to 3.7 ppb with UV detection without any pretreatment procedure.

Analysis of carboxylic acid metabolites from the tricarboxylic acid cycle in Bacillus subtilis cell extract by capillary electrophoresis using an indirect photometric detection method

With a growing interest in metabolome analysis, there is a need for developing robust methods for analysis of intracellular metabolites profiles in real samples like e.g., bacteria cell. Due to their weak absorbance properties, tri- and dicarboxylic acids from TCA cycle (citric, isocitric, 2-oxoglutaric, succinic, fumaric, malic) as well as carboxylic acid metabolites from glycolysis pathway, urea cycle and metabolism of amino compounds (formic, pyruvic, lactic, acetic, glutamic) were analyzed by capillary electrophoresis (CE) with indirect UV detection. Using 4 mM 2,6-pyridinedicarboxylic acid as a highly UV absorbing carrier electrolyte, 0.2 mM cetyltrimethylammonium bromide, 10% ethylene glycol and 10% acetonitrile, pH 3.5, carboxylic acids metabolites were analyzed in Bacillus subtilis cell extract from two different cultures: glucose and malate. CE with an electrokinetic injection mode achieved limits of detection in the range of 13-54 ppb (1.12-10(-7) - 5.96-10(-7) M). The reproducibility and linearity of method was investigated with RSD for migration time less than 1.3% and acceptable correlation coefficients. The optimized CE method was used to compare metabolome content of cell extract derived from two different culture media containing either glucose or malate as a carbon source. The changes in carboxylic acid metabolites profile were observed depending from used culture medium. Carboxylic acid concentrations ranged: in cell extract from malate culture from 59 to 0.5 microM for lactate and citrate, respectively, and in cell extract from glucose culture from 133 to 0.5 microM for glutamate and citrate, respectively. Appropriate concentrations of carboxylic acid in the single bacterium cell were estimated at mM and sub-mM levels.