Capillary electrophoretic analysis of alkaline phosphatase inhibition by theophylline

Multicolor diagnosis of salivary alkaline phosphatase triggered by silver-coated gold nanobipyramids

Alkaline phosphatase (ALP) is one of the most versatile biomarkers for early detection of several diseases, such as oral carcinomas and periodontitis; therefore, great efforts have been dedicated for developing an ALP biosensor. Multicolor detection of ALP in saliva is ideal for a point-of-care diagnosis; however, this approach is very challenging since spectral responses over wavelengths of several tens of nanometers have thus far remained difficult to achieve. In this work, a colorimetric biosensor for ALP assay has been developed based on ALP affinity to dephosphorylate glucose phosphate into glucose, which has the affinity to deposit Ag nanoshells onto Au nanobipyramids with a multicolor response. This approach provides a blue shift of localized surface plasmon resonance (LSPR) as large as 190 nm corresponding to distinctive color changes, from yellowish brown to red based on the thickness of the formed Ag shell around the Au nanobipyramids. The change in the LSPR has been conducted for highly sensitive quantitative bioassay of ALP with a detectable multicolor change with linear dynamic range of 0.1-20 U/L and low limit of detection (LOD) of 0.085 U/L. Furthermore, the developed multicolor ALP biosensor exhibits high selectivity with high recovery of 98.6% demonstrating  its reliability and suitability for a point-of-care diagnosis.

A colorimetric alkaline phosphatase biosensor based on p-aminophenol-mediated growth of silver nanoparticles

Alkaline phosphatase (ALP) is an enzyme that catalyzes the dephosphorylation of proteins, nucleic acids, and biomolecules. It is a potential biomarker for diverse diseases such as breast cancer, osteopenia, and hepatobiliary. Herein, we developed a colorimetric sensor for the ALP assay based on its enzymatic activity to dephosphorylate the p-aminophenol phosphate (pAPP) into pAP. In a solution containing silver nanoparticles (AgNPs) and Ag⁺ ions prepared using a low concentration of NaBH₄, pAP mediates the growth of AgNPs by reducing the concentration of Ag⁺ ions to enhance the intensity of localized surface plasmon resonance as the pAPP cannot induce a reduction of the remaining Ag⁺ due to the masking of the hydroxyl with phosphate. The quantitative assay of the ALP was demonstrated via the colorimetric detection of the pAP-mediated growth of AgNPs in the presence of an ALP. The highly sensitive enzymatic growth of AgNPs provided a wider dynamic linear range of 0.5-225 U/L with a lower limit of detection of 0.24 U/L than that previously reported. The use of pAP resulted in excellent selectivity of the sensor for the ALP assay in human serum, yielding a high recovery rate and a high precision of 99.2 ± 1.5 % for the standard addition method.

Kinetic analysis of the transphosphorylation with creatine kinase by pressure-assisted capillary electrophoresis/dynamic frontal analysis

Kinetic reactions of the transphosphorylation with creatine kinase (CK) were individually investigated between creatine (Cr) and creatine phosphate (CrP) by pressure-assisted capillary electrophoresis/dynamic frontal analysis (pCE/DFA). The transphosphorylations are reversible between Cr and CrP, and reverse reactions inevitably accompany in general batch analyses. In pCE/DFA, the kinetic reaction proceeds in a separation capillary and the product is continuously resolved from the substrate zone. Therefore, the formation rate is kept constant at the substrate zone without the reverse reaction, and the product is detected as a plateau signal. This study demonstrates the direct and individual analyses of both the forward and the backward kinetic reactions with CK by pCE/DFA. A plateau signal was detected in the pCE/DFA with ADP or ATP as one of the products on either the forward or the backward reactions. The Michaelis-Menten constants of K_m,ATP (from Cr to CrP) and K_m,ADP (from CrP to Cr) were successfully determined through the plateau signal. Determined values of K_m,ATP and K_m,ADP by pCE/DFA were smaller than the ones obtained by the pre-capillary batch analyses. The results agree with the fact that the reverse reaction is excluded in the analysis of the kinetic reactions. The proposed pCE/DFA is useful on individual analyses of both forward and backward kinetic reactions without any interference from the reverse reaction.

Kinetic analysis of an enzymatic hydrolysis of p-nitrophenyl acetate with carboxylesterase by pressure-assisted capillary electrophoresis/dynamic frontal analysis

An enzymatic hydrolysis of p-nitrophenyl acetate with carboxylesterase was analyzed by capillary electrophoresis/dynamic frontal analysis (CE/DFA). A plateau signal was expected with the anionic product of p-nitrophenol by the CE/DFA applying in-capillary reaction and the continuous CE resolution of the product from the substrate zone. However, the plateau height was not sufficient, and/or the plateau signal fluctuated and drifted. Therefore, a pressure assist was utilized in the CE/DFA to detect the product zone fast and to average the fluctuated plateau signal by mixing in a laminar flow. The plateau signal became relatively flat and its height was developed by the pressure-assisted capillary electrophoresis/dynamic frontal analysis (pCE/DFA). The plateau height was used for the Michaelis-Menten analysis, and a Michaelis-Menten constant was determined as KM = 0.83 mmol L-1. An enzyme inhibition was also examined with bis(p-nitrophenyl) phosphate by adding it in the separation buffer. The height of the plateau signal decreased by the inhibition, and a 50% inhibitory concentration was determined as IC50 = 0.79 μmol L-1. The values of KM and IC50 obtained in this study agreed well with the reported values. Since the proposed pCE/DFA includes electrophoretic migration of the substrate zone in a capillary, it is also noticed that the deactivation of the enzyme by ethanol on the preparation of the substrate solution can be avoided, as well as the exclusion of the inhibition by the product.

Kinetic analysis of substrate competition in enzymatic reactions with β-D-galactosidase by capillary electrophoresis / dynamic frontal analysis

Competitive inhibition between two substrates with an enzyme is investigated by capillary electrophoresis/dynamic frontal analysis (CE/DFA). Enzymatic hydrolyses of o-nitrophenyl β-D-galactopyranoside and p-nitrophenyl β-D-galactopyranoside with β-D-galactosidase were examined as a model competitive reaction. A sample solution containing the two substrates was injected into a capillary filled with a separation buffer containing an enzyme. Enzymatic hydrolysis occurred during the electrophoresis, and the products of o-nitrophenol and p-nitrophenol were continuously formed and resolved from the sample zone. Two-steps plateau signal was detected with the two-substrate solutions based on the difference in the effective electrophoretic mobility of o-nitrophenol and p-nitrophenol. Michaelis-Menten constants and inhibition constants were determined with the plateau heights. Usefulness of CE/DFA on competitive inhibition analysis is demonstrated in this study.

Capillary Electrophoresis/Dynamic Frontal Analysis for the Enzyme Assay of 4-Nitrophenyl Phosphate with Alkaline Phosphatase

A substrate of 4-nitrophenyl phosphate was enzymatically hydrolyzed by alkaline phosphatase (ALP) in a capillary tube, while an injected zone of the substrate was electrophoretically migrating in the separation buffer containing the enzyme by capillary electrophoresis (CE). During CE migration of the substrate from the start time of the electrophoresis to the detection time of the substrate, the substrate was continuously hydrolyzed by ALP to form a product of 4-nitrophenolate, and a plateau signal of 4-nitrophenolate was detected as a result of the zero-order kinetic reaction. The height of the plateau signal was directly related to the reaction rate, and it was used for the determination of a Michaelis-Menten constant through Lineweaver-Burk plots. Since the plateau signal is attributed to the dynamic formation of the product by the enzymatic reaction in CE, this analysis method is named as capillary electrophoresis/dynamic frontal analysis (CE/DFA). In CE/DFA, the CE separation is included on detecting the plateau signal, and the hydrolysis product before the sample injection is resolved from the dynamically and continuously formed product. The inhibition of the enzyme with the product is also eliminated in CE/DFA by the CE separation.

Capillary electrophoresis-based assay of phosphofructokinase-1

An assay was developed for phosphofructokinase-1 (PFK-1) using capillary electrophoresis (CE). In the glycolytic pathway, this enzyme catalyzes the rate-limiting step from fructose-6-phosphate and magnesium-bound adenosine triphosphate (Mg-ATP) to fructose-1,6-bisphosphate and magnesium-bound adenosine diphosphate (Mg-ADP). This enzyme has recently become a research target because of the importance of glycolysis in cancer and obesity. The CE assay for PFK-1 is based on the separation and detection by ultraviolet (UV) absorbance at 260 nm of Mg-ATP and Mg-ADP. The separation was enhanced by the addition of Mg²⁺ to the separation buffer. Inhibition studies of PFK-1 by aurintricarboxylic acid and palmitoyl coenzyme A were also performed. An IC₅₀ value was determined for aurintricarboxylic acid, and this value matched values in the literature obtained using coupled spectrophotometric assays. This assay for PFK-1 directly monitors the enzyme-catalyzed reaction, and the CE separation reduces the potential of spectral interference by inhibitors.

An enzyme immobilized microassay in capillary electrophoresis for characterization and inhibition studies of alkaline phosphatases

A simple and fast dynamically coated capillary electrophoretic method was developed for the characterization and inhibition studies of alkaline phosphatases(EC 3.1.3.1). An inside capillary enzymatic reaction was performed, and hydrolysis of the substrate 4-nitrophenylphosphate to 4-nitrophenol was measured. Fused-silica capillary surface was dynamically modified with polycationic polybrene coating. By reversal of the electroosmotic flow (EOF), analysis time was reduced up to 3 min as the anionic analytes were migrated in the same direction as the EOF. Furthermore, the sensitivity of the method was increased using electroinjection through high-field amplified injection. The baseline separation of 4-nitrophenylphosphate and 4-nitrophenol was achieved by employing 50 mM sodium phosphate as the running buffer (pH 8.5), 0.0025% polybrene, and a constant voltage of -15 kV, and the products were detected at 322 nm. Under the optimized conditions, a good separation with high efficiency was achieved. The new method was applied to study enzyme kinetics and inhibitor screening. K(m) and K(i) values obtained with the new CE method were compared well with the standard spectrophotometric method. Dynamic coating of fused-silica capillary gave fast and reproducible separation of substrate and product. The method can be easily optimized for inhibition studies of other isozymes.

Improved peak capacity for CE separations of enzyme inhibitors with activity-based detection using magnetic bead microreactors

A technique for separating and detecting enzyme inhibitors was developed using CE with an enzyme microreactor. The on-column enzyme microreactor was constructed using NdFeB magnet(s) to immobilize alkaline phosphatase-coated superparamagnetic beads (2.8 microm diameter) inside a capillary before the detection window. Enzyme inhibition assays were performed by injecting a plug of inhibitor into a capillary filled with the substrate, AttoPhos. Product generated in the enzyme microreactor was detected by LIF. Inhibitor zones electrophoresed through the capillary, passed through the enzyme microreactor, and were observed as negative peaks due to decreased product formation. The goal of this study was to improve peak capacities for inhibitor separations relative to previous studies, which combined continuous engagement electrophoretically mediated microanalysis and transient engagement electrophoretically mediated microanalysis to study enzyme inhibition. The effects of electric field strength, bead injection time and inhibitor concentrations on peak capacity and peak width were investigated. Peak capacities were increased to >or=20 under optimal conditions of electric field strength and bead injection time for inhibition assays with arsenate and theophylline. Five reversible inhibitors of alkaline phosphatase (theophylline, vanadate, arsenate, L-tryptophan and tungstate) were separated and detected to demonstrate the ability of this technique to analyze complex inhibitor mixtures.

Application of artificial neural networks in the prediction of product distribution in electrophoretically mediated microanalysis

The successful application of artificial neural networks toward the prediction of product distribution in electrophoretically mediated microanalysis is presented. To illustrate this concept, we examined the factors and levels required for optimization of reaction conditions for the conversion of nicotinamide adenine dinucleotide to nicotinamide adenine dinucleotide, reduced form by glucose-6-phosphate dehydrogenase in the conversion of glucose-6-phosphate to 6-phosphogluconate. A full factorial experimental design examining the factors voltage, enzyme concentration, and mixing time of reaction was utilized as input-output data sources for suitable artificial neural networks training for prediction purposes. This approach proved successful in predicting optimal values in a reduced number of experiments. Model validation addressing the extent of reaction and product ratios were subsequently determined experimentally in replicate analyses, with results shown to be in good agreement (<10% discrepancy difference) with predicted data.

Luminescent lanthanide complexes as probes for the determination of enzyme activities

The determination of enzyme activities and the screening of enzyme regulators is a major task in clinical chemistry and the development of new drugs. A broad variety of enzymatic reactions is associated with the consumption or formation of small molecules like H(2)O(2), ATP, pyrophosphate, or phosphate. Luminescent lanthanide complexes can be applied to monitor these enzymatic conversions and therefore can serve as probes for the determination of enzyme activities. The utility of this concept will be demonstrated by means of some selected examples including europium and terbium complexes. Accordingly, this new approach could be already implemented for the determination of glucose oxidase, catalase, and peroxidase activity. In particular, enzymes that catalyze phosphorylation or dephosphorylation reactions came to the fore of interest because of their high relevance as drug targets. These include (protein) kinases, adenylyl cyclases, phosphodiesterases, phosphatases, and ATPases. The development and design of fluorescent lanthanide complexes should lead to probes with optimized selectivity and response times that can be applied for high-throughput screening of enzyme inhibitors and for real-time monitoring of enzyme kinetics. In contrast to other assays for enzyme activity determination, this method does not require the use of radioactively labelled substrates or the accomplishment of rather complex and expensive immunoassays.

Response surface examination of the relationship between experimental conditions and product distribution in electrophoretically mediated microanalysis

This work presents the first known use of response surface methodology (RSM) in electrophoretically mediated microanalysis. This concept is demonstrated by examining the optimization of reaction conditions for the conversion of nicotinamide adenine dinucleotide to nicotinamide adenine dinucleotide, reduced form by glucose-6-phosphate dehydrogenase (G6PDH, EC 1.1.1.49) in the conversion of glucose-6-phosphate to 6-phosphogluconate. Experimental factors including voltage, enzyme concentration, and mixing time of reaction at the applied voltage were selected at three levels and tested in a Box-Behnken response surface design. Upon migration in a capillary under CE conditions, plugs of substrate and enzyme are injected separately in buffer and allowed to react at variable conditions. Extent of reaction and product ratios were subsequently determined by CE. The model predicted results are shown to be in good agreement (7.1% discrepancy difference) with experimental data. The use of chemometric RSM provides a direct relationship between electrophoretic conditions and product distribution of microscale reactions using CE, thereby offering a new and versatile approach to optimizing enzymatic experimental conditions.

Time-Resolved Fluorescence-Based Assay for the Determination of Alkaline Phosphatase Activity and Application to the Screening of Its Inhibitors

A single-step end point method is presented for determination of the activity of the enzyme alkaline phosphatase (ALP) using the effect of enhancement of fluorescence of the easily accessible europium(III)-tetracycline 3:1 complex (Eu3TC). Its luminescence, peaking at 616 nm if excited at 405 nm, is enhanced by a factor of 2.5 in the presence of phosphate. Phenyl phosphate was used as a substrate that is enzymatically hydrolyzed to form phenol and phosphate. The latter coordinates to Eu3TC and enhances its luminescence intensity as a result of the displacement of water from the inner coordination sphere of the central metal. The assay is performed in a time-resolved (gated) mode, which is shown to yield larger signal changes than steady-state measurement of fluorescence. The limit of detection for ALP is 4 µmol L—1. Based on this scheme, a model assay for theophylline as inhibitor for ALP was developed with a linear range from 14 to 68 µmol L— 1 of theophylline. ( Journal of Biomolecular Screening 2008:9-16)

Study of substrate inhibition by electrophoretically mediated microanalysis in partially filled capillary

Substrate inhibition is a common phenomenon in enzyme kinetics. We report here for the first time its study by a combination of the electrophoretically mediated microanalysis (EMMA) methodology with a partial filling technique. In this setup, the part of capillary is filled with the buffer best for the enzymatic reaction whereas, the rest of the capillary is filled with the background electrolyte optimal for separation of substrates and products. In the case of haloalkane dehalogenase, a model enzyme selected for this study, the enzymatic reaction was performed in 20 mM glycine buffer (pH 8.6) whereas 20 mM beta-alanine-hydrochloric acid buffer (pH 3.5) was used as a background electrolyte in combination with direct detection at 200 nm. The whole study was performed on poorly soluble brominated substrate--1,2-dibromoethane. As a result it was first necessary to find the compromise between the concentrations of the enzyme and the substrate preserving both the adequate sensitivity of the assay and at the same time the attainable substrate solubility. By means of the developed EMMA methodology we were able to determine the Michaelis constant (K(M)) as well as the substrate inhibition constant (K(SI)). The value of K(M) and K(SI) obtained were 7.7+/-2.5 mM and 1.1+/-0.4 mM, respectively. Observation of the substrate inhibition of haloalkane dehalogenase by 1,2-dibromoethane is in accordance with previous literature data.

Screening of acetylcholinesterase inhibitors in natural extracts by CE with electrophoretically mediated microanalysis technique

An electrophoretically mediated microanalysis (EMMA) method for screening acetylcholinesterase (AChE) inhibitors in natural extracts is described. In this method, solutions of AChE and the mixture of the substrate and the natural extract were successively injected into the capillary, and mixed electrophoretically by applying a voltage for a short time. Afterwards the voltage was reapplied to separate the product from the unreacted substrate and the natural extract. The measured peak area of the product at UV 230 nm represents the enzyme activity. Since the extract is mixed with the substrate, there is no need to separate the components before testing the inhibition. The inhibitory activity of the natural extract as a whole can be easily found if the peak area of the product is reduced. This makes the present method suitable for screening inhibitors in complex mixtures, such as natural extracts. Compared to the commonly used spectrometric method for screening of AChE inhibitors, the major advantage of the present method is the elimination of Ellman reagent, which is essential for the spectrometric method. This not only simplifies the experimental procedure but also minimizes false-positive results. Moreover, it is an obvious advantage of combining the separation power with the on-column enzyme assay for further investigating which compound(s) is/are responsible for the inhibition. The method was validated using a commercially available AChE inhibitor tacrine and a small chemical library containing four AChE inhibitors and 32 natural extracts. Inhibitors in natural extracts were identified with the present method.

Flow injection system for potentiometric determination of alkaline phosphatase inhibitors

A simple flow injection system for potentiometric detection of alkaline phosphatase (ALP) activity has been developed and adapted for determination of selected inhibitors of this enzyme. In this system monofluorophosphate (MFP) has been applied as a specific ALP substrate. The use of this substrate enables application of fluoride ion selective electrode (FISE) as a detector of the product of the enzyme catalyzed reaction. Moreover, chemical stability and low cost of MFP enables the use of the substrate as a component of the carrier. This way, fluoride ions contained in this substrate define and stabilize baseline signal generated by the detector. Effects from several potential ALP inhibitors and interfering species were studied and discussed. The system allows inhibitive detection of beryllium and vanadate ions at ppb levels with relatively high selectivity, short time of analysis and high throughput of the system (near 8 samples h(-1)).

Development of off-line and on-line capillary electrophoresis methods for the screening and characterization of adenosine kinase inhibitors and substrates

Fast and convenient CE assays were developed for the screening of adenosine kinase (AK) inhibitors and substrates. In the first method, the enzymatic reaction was performed in a test tube and the samples were subsequently injected into the capillary by pressure and detected by their UV absorbance at 260 nm. An MEKC method using borate buffer (pH 9.5) containing 100 mM SDS (method A) was suitable for separating alternative substrates (nucleosides). For the CE determination of AMP formed as a product of the AK reaction, a phosphate buffer (pH 7.5 or 8.5) was used and a constant current (95 microA) was applied (method B). The methods employing a fused-silica capillary and normal polarity mode provided good resolution of substrates and products of the enzymatic reaction and a short analysis time of less than 10 min. To further optimize and miniaturize the AK assays, the enzymatic reaction was performed directly in the capillary, prior to separation and quantitation of the product employing electrophoretically mediated microanalysis (EMMA, method C). After hydrodynamic injection of a plug of reaction buffer (20 mM Tris-HCl, 0.2 mM MgCl2, pH 7.4), followed by a plug containing the enzyme, and subsequent injection of a plug of reaction buffer containing 1 mM ATP, 100 microM adenosine, and 20 microM UMP as an internal standard (I.S.), as well as various concentrations of an inhibitor, the reaction was initiated by the application of 5 kV separation voltage (negative polarity) for 0.20 min to let the plugs interpenetrate. The voltage was turned off for 5 min (zero-potential amplification) and again turned on at a constant current of -60 microA to elute the products within 7 min. The method employing a polyacrylamide-coated capillary of 20 cm effective length and reverse polarity mode provided good resolution of substrates and products. Dose-response curves and calculated K(i) values for standard antagonists obtained by CE were in excellent agreement with data obtained by the standard radioactive assay.

Determination of enzymatic activity by capillary electrophoresis

Enzymes are biological catalysts that play an important role in biochemical reactions necessary for normal growth, maturation and reproduction through whole live world. Their accurate quantitation in biological samples is important in many fields of biochemistry, not only in routine biochemistry and in fundamental research, but also in clinical and pharmacological research and diagnosis. Since the direct measurement of enzymes by masses is impossible, they must be quantified by their catalytic activities. Many different methods have been applied for this purpose so far. Although photometric methods are undoubtedly the most frequently used, separation methods will further gain their position in this field. The article reviews different possibilities for the assay of enzymatic activity by means of capillary electrophoresis (CE). Both the off-line and on-line enzyme assays based on CE are discussed.

A capillary electrophoresis method for the characterization of ecto-nucleoside triphosphate diphosphohydrolases (NTPDases) and the analysis of inhibitors by in-capillary enzymatic microreaction

A capillary electrophoresis (CE) method for the characterization of recombinant NTPDases 1, 2, and 3, and for assaying NTPDase inhibitors has been developed performing the enzymatic reaction within the capillary. After hydrodynamic injection of plugs of substrate solution with or without inhibitor in reaction buffer, followed by a suspension of an enzyme-containing membrane preparation, and subsequent injection of another plug of substrate solution with or without inhibitor, the reaction took place close to the capillary inlet. After 5 min, the electrophoretic separation of the reaction products was initiated by applying a constant current of -60 muA. The method employing a polyacrylamide-coated capillary and reverse polarity mode provided baseline resolution of substrates and products within a short separation time of less than 7 min. A 50 mM phosphate buffer (pH 6.5) was used for the separations and the products were detected by their UV absorbance at 210 nm. The Michaelis-Menten constants (K (m)) for the recombinant rat NTPDases 1, 2, and 3 obtained with this method were consistent with previously reported data. The inhibition studies revealed pronounced differences in the potency of reactive blue 2, pyridoxalphosphate-6-azophenyl-2',4'-disulfonic acid (PPADS), suramin, and N (6)-diethyl-beta,gamma-dibromomethylene-ATP (ARL67156) towards the NTPDase isoforms. Notably, ARL67156 does not inhibit all NTPDases, having only a minor inhibitory effect on NTPDase2. Dipyridamole is not an inhibitor of the NTPDase isoforms investigated. The new method is fast and accurate, it requires only tiny amounts of material (nanoliter scale), no sample pretreatment and can be fully automated; thus it is clearly superior to the current standard methods.

Increasing the efficiency of in-capillary electrophoretically mediated microanalysis reactions via rapid polarity switching

We report herein a new approach to enhance the sensitivity or speed of CE-based methods that involve in-line reactions. Rapid polarity switching (RPS) is used as a novel means for in-line mixing of two reactant solutions via rapid (1-5 s) and sequential switching of the applied potential field. By employing the RPS approach with a model chemical reaction, that between creatinine and alkaline picrate, significant enhancement in sensitivity (or a decrease in analysis time) is realized. Both increased convection and electrophoretic stacking of the ionic reagent appear to contribute to the rise in apparent reaction rate. When coupled with in-line chemistry of the Jaffe method for creatinine, the RPS methodology allows for 3-fold faster determination of creatinine in the concentration range needed for the analysis of clinical blood serum specimens. The new approach also allows the analysis to be performed without the need for the cumbersome and problematic enhanced sensitivity cell.

Study of enzyme kinetics of phenol sulfotransferase by electrophoretically mediated microanalysis

Electrophoretically mediated microanalysis (EMMA) was applied for the study of the kinetic parameters of the enzymatic reaction of phenol sulfotransferase SULT1A1 isoenzyme with 4-nitrophenol as a substrate. The SULT1A1 activity was determined by the quantitation of the product, 4-nitrophenyl sulfate, at 274 nm by using different injection and separation steps. This new approach solved the problem of the presence of the very strong inhibitor, adenosine 3',5'-bisphosphate (PAP), in the co-substrate solution (adenosine 3'-phosphate 5'-phosphosulfate, PAPS) which is unstable at room temperature. The inhibitor PAP was electrophoretically separated from the co-substrate PAPS before the injection of enzyme and substrate inside the capillary (and thus before their in-capillary encountering). With the developed in-capillary SULT1A1 activity assay an average Michaelis constant (Km) for 4-nitrophenol was calculated to be 0.84 microM, a value which is consistent with a previously reported value. Strong substrate inhibition (above a 4-nitrophenol concentration of 2.5 microM) was observed, and this is also in accordance with literature values.

Inhibition study of angiotensin converting enzyme by capillary electrophoresis after enzymatic reaction at capillary inlet

Capillary electrophoresis was used to study the inhibition of angiotensin-converting enzyme (ACE) by different inhibitors. Reaction occurred at the capillary inlet during a predetermined waiting period, followed by the electrophoretic separation of the reaction compounds. ACE activity was determined by the quantification of the reaction product, hippuric acid, at 230 nm. The technique was used to study the potency of five different inhibitors (captopril, lisinopril, perindoprilat, quinaprilat and benazeprilat). During a kinetic study, the Ki value of captopril was estimated to be 55.4 +/- 8.8 nM, a value consistent with previously reported values.

Electrophoretically mediated microanalysis

This review describes the existing developments in the use of the capillary electrophoretic microanalytical technique for the in-line study of enzyme reaction, electrophoretically mediated microanalysis (EMMA). The article is divided into a number of parts. After an introduction, the different modes, basic principle, procedure, and some mathematical treatments of EMMA methodology are discussed and illustrated. The applications of EMMA for enzyme assay and for non-enzymatic determination are summarized into two tables. In addition to classical capillary electrophoresis (CE) instrument EMMA, special emphasis is given to a relatively new technique: EMMA on CE microchip. Finally, conclusions are drawn.

Determination of lactate or oxalate using injected lactate oxidase and peroxidase by capillary electrophoresis with UV detection

Two reactions, catalyzed by lactate oxidase (LO) and peroxidase, are initiated by a single injection of the enzymes and the substrate 2,2'-azino-bis(3-ethylene-thiazoline-6-sulfonic acid) (ABTS) into the capillary previously filled with the sample (lactate or lactate-oxalate mixture) and the run buffer containing NADH. The oxidized ABTS product upon reaction with NADH is converted to NAD(+) which is separated and detected in less than 2 min at 266 nm with a sample throughput of 7 min (including wash steps between samples). Simplex trade mark software is used to optimize the enzyme concentrations and reaction temperature. Consumption of the more expensive LO enzyme is only 1.4 x 10(-3) U per assay assuming 27 nL per injection. Linearity is established within the range from 0.0025 to 1 mM with R(2) of 0.9982. Recoveries of lactate from five spiked serum samples averaged 101%. Application of this method for the determination of oxalate as an inhibitor of LO is demonstrated.

Inhibition study of rhodanese by means of electrophoretically mediated microanalysis

A combination of the electrophoretically mediated microanalysis methodology with a partial filling technique was applied for the inhibition study of bovine liver rhodanese by 2-oxoglutarate. In this set-up, part of the capillary is filled with the best buffer for the enzymatic reaction, while the rest of the capillary is filled with the optimal background electrolyte for separation of substrates and products. The estimated value of K1 for 2-oxoglutarate was 3.62 x 10(-4) +/- 1.43 x 10(-4) M with respect to cyanide and 1.40 x 10(-3) +/- 1.60 x 10(-4) M with respect to thiosulfate. In addition, the type of inhibition was also evaluated. The findings of 2-oxoglutarate as the competitive inhibitor with respect to cyanide and as the uncompetitive inhibitor with respect to thiosulfate are in accordance with previous literature data.

Enzyme inhibition-based biosensors and biosensing systems: questionable analytical devices

An overview of methods based on enzyme inhibition is presented. Both biosensors and biosensing systems (implemented in continuous and discontinuous approaches) are considered. The aim of the overview is to alert users on the use of these devices which, despite they can involve selective biocatalysts, the inhibition effect is not selective. Tables and examples illustrate this assertion.

Kinetic study of angiotensin converting enzyme activity by capillary electrophoresis after in-line reaction at the capillary inlet

The in-capillary reaction of angiotensin converting enzyme (ACE) with the tripeptide substrate hippuryl-L-histidyl-L-leucine was studied. ACE activity was determined by the quantitation of the product, hippuric acid, at 230 nm. Reaction occurred at the capillary inlet during a predetermined waiting period, followed by the electrophoretic separation of the compounds. When the set-up was reversed, i.e. reaction at the opposite side after short-end injection of enzyme and substrate, separation was achieved in less than 5 min. Using the Lineweaver-Burk equation, an average Michaelis constant for ACE from rabbit lung was calculated to be 1.16 +/- 0.12 mM, a value consistent with previously reported data.

Kinetic study of gamma-glutamyltransferase activity by electrophoretically mediated microanalysis combined with micellar electrokinetic capillary chromatography

The use of capillary electrophoresis for the determination of gamma-glutamyltransferase (GGT) activity with gamma-glutamyl-p-nitroanilide (Glu-p-NA) as a substrate was investigated. The reaction velocity was quantified spectrophotometrically by the corrected peak area of the product p-nitroaniline (pNA) at 380 nm. Micelles composed of sodium deoxycholic acid were used in the background electrolyte in order to obtain a baseline separation between the substrate and the product. The presence of the micelles did not influence the enzymatic reaction. The electrophoretic system was used, not only for the separation and quantitation of the different reaction compounds but also for the in-capillary mixing of the enzyme and substrate plugs. This methodology is known as electrophoretically mediated microanalysis (EMMA). With the developed in-capillary activity assay an average Michaelis constant (K(M)) for GGT was calculated to be 2.09 mM (RSD = 7.3%, n = 3), a value consistent with previously reported values.

Studies of reversible inhibition, irreversible inhibition, and activation of alkaline phosphatase by capillary electrophoresis

Reversible inhibition, irreversible inhibition, and activation of calf intestinal alkaline phosphatase (EC 3.1.3.1) have been studied by capillary electrophoresis. The capillary electrophoretic enzyme-inhibitor assays were based on electrophoretic mixing of inhibitor and enzyme zones in a substrate-filled capillary. Enzyme inhibition was indicated by a decrease in product formation detected in the capillary by laser-induced fluorescence. Reversible enzyme inhibitors could be quantified by Michaelis-Menten treatment of the electrophoretic data. Reversible, competitive inhibition of alkaline phosphatase by sodium vanadate and sodium arsenate has been examined, and reversible, noncompetitive inhibition by theophylline has been studied. The K(i) values determined for these reversible inhibitors using capillary electrophoresis are within the range of values reported in the literature for the same enzyme-inhibitor combinations. Irreversible inhibition of alkaline phosphatase by EDTA at concentrations of 1.0mM and above has been observed. Activation of alkaline phosphatase has also been observed for EDTA at concentrations from 20 to 400 microM.

Capillary electrophoresis of proteins 1999-2001

This review article with 223 references describes recent developments in capillary electrophoresis (CE) of proteins and covers papers published during last two years, from the previous review (V. Dolnik, Electrophoresis 1999, 20, 3106-3115) through Spring 2001. It describes the topics related to CE of proteins including modeling of the electrophoretic properties of proteins, sample pretreatment, wall coatings, improving selectivity, detection, special electrophoretic techniques, and applications.