A microchip-based enzyme assay for protein kinase A

Digital Microfluidics Chips for the Execution and Real-Time Monitoring of Multiple Ribozymatic Cleavage Reactions

In this paper, we describe the design and performance of two digital microfluidics (DMF) chips capable of executing multiple ribozymatic reactions, with proper controls, in response to short single-stranded DNA inducers. Since the fluorescence output of a reaction is measurable directly from the chip, without the need for gel electrophoresis, a complete experiment involving up to eight reactions (per chip) can be carried out reliably, relatively quickly, and efficiently. The ribozymes can also be used as biosensors of the concentration of oligonucleotide inputs, with high sensitivity, low limits of quantification and of detection, and excellent signal-to-noise ratio. The presented chips are readily usable devices that can be used to automate, speed up, and reduce the costs of ribozymatic reaction experiments.

Development of a Potent and Specific FGFR4 Inhibitor for the Treatment of Hepatocellular Carcinoma

Abnormal activation of the fibroblast growth factor 19 (FGF19)/fibroblast growth factor receptor 4 (FGFR4) signaling pathway has been shown to drive the proliferation of a significant portion of hepatocellular carcinoma (HCC). Resistance and toxicity are serious drawbacks that have been observed upon use of the current first- and second-line treatment options for HCC, therefore warranting the investigation of alternative therapeutic approaches. We report the development and biological characterization of a covalent inhibitor that is highly potent and exquisitely specific to FGFR4. The crystal structure of this inhibitor in complex with FGFR4 was solved, confirming its covalent binding and revealing its binding mode. We also describe the first clickable probe for FGFR4 that can be used to directly measure target engagement in cells. Our compound exhibited great antitumor activity in HCC cell lines and tumor xenograft models. These results provide evidence of a promising therapeutic lead for the treatment of a subset of HCC patients.

Effect of localized hypoxia on Drosophila embryo development

Environmental stress, such as oxygen deprivation, affects various cellular activities and developmental processes. In this study, we directly investigated Drosophila embryo development in vivo while cultured on a microfluidic device, which imposed an oxygen gradient on the developing embryos. The designed microfluidic device enabled both temporal and spatial control of the local oxygen gradient applied to the live embryos. Time-lapse live cell imaging was used to monitor the morphology and cellular migration patterns as embryos were placed in various geometries relative to the oxygen gradient. Results show that pole cell movement and tail retraction during Drosophila embryogenesis are highly sensitive to oxygen concentrations. Through modeling, we also estimated the oxygen permeability across the Drosophila embryonic layers for the first time using parameters measured on our oxygen control device.

Characterization of PKACα enzyme kinetics and inhibition in an HPLC assay with a chromophoric substrate

Here we describe a convenient, inexpensive, and non-hazardous method for the measurement of the kinase activity of the catalytic subunit of cAMP-dependent protein kinase (PKACα). The assay is based on the separation of a substrate peptide labeled with a strong chromophore from the phosphorylated product peptide by high-performance liquid chromatograph (HPLC) and quantification of the product ratiometrically at a wavelength in the visual spectrum (Vis). The utility and reliability of the HPLC-Vis assay were demonstrated by characterizing the kinetic parameters (KM, Vmax) of the new Rh-MAB-Kemptide substrate, a commercially prepared TAMRA-Kemptide substrate, and ATP as well as the potency (IC50, Ki) of the known PKACα inhibitors H89 and PKI(5-24). The advantages of this assay are that it is convenient and inexpensive, uses readily synthesized or commercially available substrates that are shelf-stable, uses a common piece of laboratory equipment, and does not require any hazardous materials such as radioactive γ-32P-ATP. The assay format is also highly flexible and could be adapted for the testing of many different kinases by changing the peptide substrate sequence.

Measuring Kinase Activity-A Global Challenge

The kinase enzymes within a cell, known collectively as the kinome, play crucial roles in many signaling pathways, including survival, motility, differentiation, stress response, and many more. Aberrant signaling through kinase pathways is often linked to cancer, among other diseases. A major area of scientific research involves understanding the relationships between kinases, their targets, and how the kinome adapts to perturbations of the cellular system. This review will discuss many of the current and developing methods for studying kinase activity, and evaluate their applications, advantages, and disadvantages. J. Cell. Biochem. 118: 3595-3606, 2017. © 2017 Wiley Periodicals, Inc.

Screening applications in drug discovery based on microfluidic technology

Microfluidics has been the focus of interest for the last two decades for all the advantages such as low chemical consumption, reduced analysis time, high throughput, better control of mass and heat transfer, downsizing a bench-top laboratory to a chip, i.e., lab-on-a-chip, and many others it has offered. Microfluidic technology quickly found applications in the pharmaceutical industry, which demands working with leading edge scientific and technological breakthroughs, as drug screening and commercialization are very long and expensive processes and require many tests due to unpredictable results. This review paper is on drug candidate screening methods with microfluidic technology and focuses specifically on fabrication techniques and materials for the microchip, types of flow such as continuous or discrete and their advantages, determination of kinetic parameters and their comparison with conventional systems, assessment of toxicities and cytotoxicities, concentration generations for high throughput, and the computational methods that were employed. An important conclusion of this review is that even though microfluidic technology has been in this field for around 20 years there is still room for research and development, as this cutting edge technology requires ingenuity to design and find solutions for each individual case. Recent extensions of these microsystems are microengineered organs-on-chips and organ arrays.

Protein Kinase Selectivity Profiling Using Microfluid Mobility Shift Assays

Biochemical selectivity profiling is an integral part of early drug development. Typically compounds from optimization phase are regularly tested for off-target activities within or across target families. This article presents workflow and critical aspects of biochemical protein kinase profiling based on microfluidic mobility shift assays.

Screening of protein kinase inhibitors in natural extracts by capillary electrophoresis combined with liquid chromatography-tandem mass spectrometry

We report a capillary electrophoresis method in conjunction with liquid chromatography-tandem mass spectrometry (LC-MS/MS) for screening of protein kinase inhibitors (PKIs) in natural extracts. Protein kinase A (PKA), substrate 5-carboxyfluorescein-labeled kemptide (CLK) and inhibitor H-89 were employed for the method development and validation. Enzymatic inhibition assay was performed with electrophoretically mediated microanalysis technique. Once the bioactivity of a natural extract was confirmed, an assay-guided isolation and structure elucidation using LC-MS/MS were accomplished to identify the compounds which are responsible for the observed bioactivity. Totally 33 natural extracts were screened with the method, and baicalin in the extract of Radix Scutellariae was identified to be a new PKI of PKA. This result demonstrated the practical applicability of our method in screening of PKIs from natural products.

Insights into the "free state" enzyme reaction kinetics in nanoconfinement

The investigation of enzyme reaction kinetics in nanoconfined spaces mimicking the conditions in living systems is of great significance. Here, a nanofluidics chip integrated with an electrochemical detector has been designed for studying "free state" enzyme reaction kinetics in nanoconfinement. The nanofluidics chip is fabricated using the UV-ablation technique developed in our group. The enzyme and substrate solutions are simultaneously supplied from two single streams into a nanochannel through a Y-shaped junction. The laminar flow forms in the front of the nanochannel, then the two liquids fully mix at their downstream where a homogeneous enzyme reaction occurs. The "free state" enzyme reaction kinetics in nanoconfinement can thus be investigated in this laminar flow based nanofluidics device. For demonstration, glucose oxidase (GOx) is chosen as the model enzyme, which catalyzes the oxidation of beta-d-glucose. The reaction product hydrogen peroxide (H2O2) can be electrochemically detected by a microelectrode aligning to the end of nanochannel. The steady-state electrochemical current responding to various glucose concentrations is used to evaluate the activity of the "free state" GOx under nanoconfinement conditions. The effect of liquid flow rate, enzyme concentration, and nanoconfinement on reaction kinetics has been studied in detail. Results show that the "free state" GOx activity increases significantly compared to the immobilized enzyme and bath system, and the GOx reaction rate in the nanochannel is two-fold faster than that in bulk solution, demonstrating the importance of "free state" and spatial confinement for the enzyme reaction kinetics. The present approach provides an effective method for exploiting the "free state" enzyme activity in nanospatial confinement.

The cat that caught the canary: what to do with single-molecule trapping

It has recently become possible to trap individual fluorescent biomolecules in aqueous solution by using real-time tracking and active feedback to suppress Brownian motion. We propose areas of investigation in which anti-Brownian electrokinetic (ABEL) trapping of single molecules is likely to lead to significant new insights into biomolecular dynamics.

Polymer-based dense fluidic networks for high throughput screening with ultrasensitive fluorescence detection

Microfluidics represents a viable platform for performing high throughput screening (HTS) because of its ability to automate fluid handling and generate fluidic networks with high number densities over small footprints appropriate for the simultaneous optical interrogation of many screening assays. While most HTS campaigns depend on fluorescence, readers typically use point detection and serially address the assay results significantly lowering throughput or detection sensitivity due to a low duty cycle. To address this challenge, we present here the fabrication of a high-density microfluidic network packed into the imaging area of a large field-of-view (FoV) ultrasensitive fluorescence detection system. The fluidic channels were 1, 5 or 10 μm (width), 1 μm (depth) with a pitch of 1-10 μm and each fluidic processor was individually addressable. The fluidic chip was produced from a molding tool using hot embossing and thermal fusion bonding to enclose the fluidic channels. A 40× microscope objective (numerical aperture=0.75) created an FoV of 200 μm, providing the ability to interrogate ∼25 channels using the current fluidic configuration. An ultrasensitive fluorescence detection system with a large FoV was used to transduce fluorescence signals simultaneously from each fluidic processor onto the active area of an electron multiplying charge-coupled device. The utility of these multichannel networks for HTS was demonstrated by carrying out the high throughput monitoring of the activity of an enzyme, apurinic Endonuclease 1, used as a model-screening assay.

Study on the kinetics of homogeneous enzyme reactions in a micro/nanofluidics device

In this paper, a micro/nanofluidic preconcentration device integrated with an electrochemical detector has been used to study the enrichment of enzymes and homogeneous enzyme reaction kinetics. The enzymes are first concentrated in front of a nanochannel via an exclusion-enrichment effect (EEE) mechanism of the nanochannel integrated in a microfluidics device. If a substrate is electrokinetically transported to the concentrated enzymes, homogeneous enzymatic reaction occurs. The enzymatic reaction product can penetrate through the nanochannel to be detected electrochemically. In this device, the enriched enzymes can be well retained and repeatedly used, thus, the enzymatic reaction occurs in a continuous-flow mode. For demonstration, Glucose oxidase (GOx) was chosen as the model enzyme to study the influence of enzyme concentration on its reaction kinetics. The different concentration of GOx in front of the nanochannel was simply achieved by using different enrichment time. When substrate glucose was introduced electrokinetically, a rapid electrochemical steady-state response could be obtained. It was found that the electrochemical response to a constant glucose concentration increased with the increase of enzyme enrichment time, which is expected for homogeneous enzymatic reactions. Under proper conditions, the electrochemical responds linearly to the glucose concentration ranging from 0 to 15 mM, and the Michaelis constants (K(m)) are relatively low, which indicates a more efficient complex formation between enzyme and substrate. These results suggest that the present micro/nanofluidics device is promising for the study of enzymatic reaction kinetics and other bioassays such as cell assays, drug discovery, and clinical diagnosis.

Bio-Microfluidics: Overview

With a view to establish unique interfacial synergistic interactions between two seemingly distant fields of microfluidics and biology, Bio-microfluidics has become a progressive arena of research in recent times. Bio-microfluidic tools in the format of lab-on-a-chip devices have been extensively utilized to uncouth hitherto un-illuminated regions of cellular-molecular biology, biotechnology and biomedical engineering. This chapter elaborately delineates the linking between the fundamental microscale physics and biologically relevant physico-chemical events and how, in practice, these relations are exploited in microfluidic devices. Finally, potential directions of future biomicrofluidic research are also discussed.

Simple device for multiplexed electrophoretic separations using gradient elution moving boundary electrophoresis with channel current detection

A new microfluidic electrophoresis device and technique is described that is designed specifically for multiplexed, high-throughput separations. The device consists of an array of short (3 mm) capillaries connecting individual sample reservoirs to a common buffer reservoir. Each capillary in the array functions as both a separation channel and as a conductivity-based detection cell. The new technique is based upon the recently described gradient elution moving boundary electrophoresis (GEMBE) technique, which uses a combination of an electric field and buffer counterflow to achieve electrophoretic separations in short capillaries or microfluidic channels. A high voltage drives electrophoresis of the sample analytes through each separation channel. At the start of a separation, the bulk counterflow of buffer through the channel is high, and none of the analytes of interest can enter the channel. The counterflow is then gradually reduced until each analyte, in turn, is able to enter the channel where it is detected as a moving boundary or step. With very short capillaries, only one step at a time is present in each capillary, and the electric current through the channels can then be used as the detector signal, without any extra detector hardware. The current vs time signal for each channel is then smoothed and differentiated to produce a set of simultaneous electropherograms. Because there is no light source or other added hardware required for detection, the system is simple and can be easily and inexpensively scaled up to perform large numbers of simultaneous analyses. As a first demonstration, a 16-channel array device is used for high-throughput, time-series measurements of enzyme activity and inhibition.

Hexokinase inhibitor screening based on adenosine 5'-diphosphate determination by electrophoretically mediated microanalysis

A CE-based method for hexokinase inhibitor screening was developed in the present paper. In this method, hexokinase activity was assayed via electrophoretically mediated microanalysis (EMMA), which combines on-column hexokinase-mediated reaction and measurement of produced adenosine 5'-diphosphate (ADP) via electrophoretical separation and UV detection. Enzyme inhibition can be read out directly from the reduced peak area of ADP in comparison with a reference electropherogram obtained in the absence of any inhibitor. Conditions for on-column enzyme reaction and separation of adenosine 5'-triphosphate (ATP) and ADP were optimized. The optimal buffer composition for enzymatic reaction was 25 mM HEPES buffer (pH 7.5) containing 5 mM MgCl(2), whereas the optimal buffer composition for separation was 100 mM Tris-phosphate buffer (pH 5.5) containing 0.02% (m/v) hexadimethrine bromide (HDB). Fortunately, discontinuous buffer system can be adapted easily in the EMMA method. The time for separation was reduced dramatically to less than 3 min by reversing the direction of EOF via dynamically coating the capillary wall with the cationic polyelectrolyte HDB. Moreover, the peak tailing of ATP was also reduced by HDB coating. The Z' factor as high as 0.98 was obtained, indicating a high quality of the screening data. The present method is simple, robust and cost-effective.

Enzyme-linked immunosorbent assay of Escherichia coli O157:H7 in surface enhanced poly(methyl methacrylate) microchannels

A novel surface treatment method was developed to enhance polymer-based microchannel enzyme-linked immunosorbent assay (ELISA) for Escherichia coli O157:H7 detection. By applying an amine-bearing polymer, poly(ethyleneimine) (PEI), onto poly(methyl methacrylate) (PMMA) surface at pH higher than 11, PEI molecules were covalently attached and their amine groups were introduced to PMMA surface. Zeta potential analysis and X-ray photoelectron spectroscopy (XPS) demonstrated that the alkali condition is preferable for PEI attachment onto the PMMA surface. The amine groups on the PMMA surface were then functionalized with glutaraldehyde, whose aldehyde groups served as the active sites for binding the antibody by forming covalent bonds with the amine groups of the protein molecules. This surface modification greatly improved antibody binding efficiency and the microchannel ELISA for E. coli O157:H7 detection. Compared with untreated PMMA microchannels, approximately 45 times higher signal and 3 times higher signal/noise ratio were achieved with the PEI surface treatment, which also shortened the time required for cells to bind to the microchannel surface to approximately 2 min, much less than that usually required for the same ELISA carried out in 96-well plates. The detection in the microchannel ELISA only required 5-8 cells per sample, which is also better than 15-30 cells required in multi-well plates. With the high sensitivity, short assay time, and small reagent consumption, the microchannel ELISA can be economically used for fast detection of E. coli O157:H7.

Determination of the activities of glutamic oxaloacetic transaminase and glutamic pyruvic transaminase in a microfluidic system

A microfluidic system for the analysis of the activities of glutamic-oxaloacetic transaminase (GOT) and glutamic-pyruvic transaminase (GPT) was fabricated. The device consists of a glass chip with a micro-electrochemical L-glutamate sensor and a polydimethylsiloxane (PDMS) sheet with a Y-shaped micro-flow channel. A sample solution and a substrate solution for the enzymes were introduced from two injection ports at the end of the flow channel. When the flows were stopped, substrates in a solution mixed immediately with either of the enzymes by diffusion in a mixing channel. L-glutamate produced by the enzymatic reaction of GOT or GPT in the flow channel was detected by using the L-glutamate sensor. A distinct current increase was observed immediately after mixing, and the initial slope of the response curve varied in proportion to the activity of GOT or GPT. The relation between the slope of the response curve and the enzyme activity was linear between 7 and 228 U l-1 for GOT and 9 and 250 U l-1 for GPT. The quality of the response curve was improved with an increase in the channel height. The measurement based on the rate analysis in the micro-flow channel facilitated the reduction of the influence of interferents. The influence of the viscosity of the sample solution was also checked for the analysis of real samples. The determination of the enzyme activities was also conducted in a system with micropumps fabricated for a sample injection. Two solutions could be mixed in the mixing channel, and the activity of the enzymes could be measured as in the experiments using microsyringe pumps.

Development of a peptide inhibitor-based cantilever sensor assay for cyclic adenosine monophosphate-dependent protein kinase

A highly sensitive nanomechanical cantilever sensor assay based on an electrical measurement has been developed for detecting activated cyclic adenosine monophosphate (cyclic AMP)-dependent protein kinase (PKA). Employing a peptide derived from the heat-stable protein kinase inhibitor (PKI), a magnetic bead system was first selected as a vehicle to immobilize the PKI-(5-24) peptide for capturing PKA catalytic subunit and the activity assay was applied for indirectly assessing the binding. Synergistic interactions of adenosine triphosphate (ATP) and the peptide inhibitor with the kinase were then investigated by a solution phase capillary electrophoretic assay, and by surface plasmon resonance technology which involved immobilization of the peptide inhibitor. After systemically evaluated by a homogeneous direct binding assay, the ATP-dependent recognition of the catalytic subunit of PKA by PKI-(5-24) was successfully transferred on to the nanomechanical cantilevers at protein concentrations of 6.6 pM-66 nM, exhibiting much higher sensitivity and wider dynamic range than the conventional activity assay. Thus, direct assessment of activated kinases using the cantilever sensor system functionalized with specific peptide inhibitors holds great promise in analytical applications and clinical medicine.

Capillary electrophoresis of signaling molecules

The emerging field of quantitative systems biology uses high-throughput bioanalytical measurements to gain a deeper understanding of biological phenomena. With the advent of instrumentation platforms, capillary electrophoresis spans a very wide range of biological applications. This short article focuses on the exploitation of capillary electrophoresis for the systems-level analysis of cell signaling molecules.

Surface modification for enhancing antibody binding on polymer-based microfluidic device for enzyme-linked immunosorbent assay

A novel surface treatment method using poly(ethyleneimine) (PEI), an amine-bearing polymer, was developed to enhance antibody binding on the poly(methyl methacrylate) (PMMA) microfluidic immunoassay device. By treating the PMMA surface of the microchannel on the microfluidic device with PEI, 10 times more active antibodies can be bound to the microchannel surface as compared to those without treatment or treated with the small amine-bearing molecule, hexamethylenediamine (HMD). Consequently, PEI surface modification greatly improved the immunoassay performance of the microfluidic device, making it more sensitive and reliable in the detection of IgG. The improvement can be attributed to the spacer effect as well as the functional amine groups provided by the polymeric PEI molecules. Due to the smaller dimensions (140x125 microm) of the microchannel, the time required for antibody diffusion and adsorption onto the microchannel surface was reduced to only several minutes, which was 10 times faster than the similar process carried out in 96-well plates. The microchip also had a wider detection dynamic range, from 5 to 1000 ng/mL, as compared to that of the microtiter plate (from 2 to 100 ng/mL). With the PEI surface modification, PMMA-based microchips can be effectively used for enzyme linked immunosorbent assays (ELISA) with a similar detection limit, but much less reagent consumption and shorter assay time as compared to the conventional 96-well plate.

Chip-based bioassay using bacterial sensor strains immobilized in three-dimensional microfluidic network

A whole-cell bioassay has been performed using Escherichia coli sensor strains immobilized in a chip assembly, in which a silicon substrate is placed between two poly(dimethylsiloxane) (PDMS) substrates. Microchannels fabricated on the two separate PDMS layers are connected via perforated microwells on the silicon chip, and thus, a three-dimensional microfluidic network is constructed in the assembly. Bioluminescent sensor strains mixed with agarose are injected into the channels on one of the two PDMS layers and are immobilized in the microwells by gelation. Induction of the firefly luciferase gene expression in the sensor strains can be easily carried out by filling the channels on the other layer with sample solutions containing mutagen. Bioluminescence emissions from each well are detected after injection of luciferin/ATP mixtures into the channels. In this assay format using two multichannel layers and one microwell array chip, the interactions between various types of samples and strains can be monitored at each well on one assembly in a combinatorial fashion. Using several genotypes of the sensor strains or concentrations of mitomycin C in this format, the dependence of bioluminescence on these factors was obtained simultaneously in the single screening procedure. The present method could be a promising on-chip format for high-throughput whole-cell bioassays.

Homogeneous time-resolved fluorescence and its applications for kinase assays in drug discovery

The rapidly growing interest in kinases as potential targets for therapeutic intervention has prompted the development of many kinase assay technologies. One exciting example is homogeneous time-resolved fluorescence (HTRF). An HTRF assay utilizes the signal generated by the fluorescence resonance energy transfer between donor and acceptor molecules in close proximity. Dual-wavelength detection helps to eliminate media interference, and the final signal is proportional to the extent of product formation. Thus far, the reported applications of this technology for in vitro kinase assays have mainly focused on high-throughput screening. In this report, we extend the applications of HTRF technology to the areas of enzyme and inhibitor characterization, some aspects of which were previously believed impossible. We describe the methods developed for determining the kinetic parameters of an enzyme, such as K(m) and k(cat), and the procedures for inhibitor mechanistic studies including ATP competitiveness and slow-binding and dissociation kinetics. These assays can be readily applied to any kinase and are valuable in advancing a program through the early stages of drug discovery.

Quantitative methods for the analysis of protein phosphorylation in drug development

Most signal transduction and cell signaling pathways are mediated by protein kinases. Protein kinases have emerged as important cellular regulatory proteins in many aspects of neoplasia. Protein kinase inhibitors offer the opportunity to target diseases such as cancer with chemotherapeutic agents specific for the causative molecular defect. In order to identify possible targets and assess kinase inhibitors, quantitative methods for analyzing protein phosphorylation have been developed. This review examines some of the current formats used for quantifying kinase function for drug development.

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.

High-throughput enzyme assay on a multichannel microchip using optically gated sample introduction

To meet the requirements for high-throughput screening for drug discovery research, it is very important to develop techniques with the ability of performing multiple enzyme assays simultaneously. Using optically gated sample introduction on a multichannel microchip, multiple enzyme assays have been demonstrated in four parallel channels. The hydrolysis of fluorescein mono-beta-D-galactopyranoside by beta-galactosidase and the inhibition of this reaction by the competitive inhibitor phenylethyl beta-D-thiogalactoside were initially studied to determine the effect of system movement using the voice coil actuator on the enzyme assay reaction. The results from these two studies are consistent with the results from the assay using a single-channel microchip, and they demonstrate that the system using optically gated sample introduction on multichannel microchip can be used to perform multiple enzyme assays. Three unique enzyme assays were also performed in different channels, which show this technique could be competitive for high-throughput screening in drug discovery with other traditional techniques.

Utilization of luminescent technology to develop a kinase assay: Cdk4 as a model system

Protocols to assess kinase activity generally include radioactive methods, fluorescent polarization technology and the use of specific antibodies. Here, a simple, effective, non radioactive method to measure kinase activity of immunoprecipitated proteins is described. Cdk4, a cell cycle dependent enzyme, was immunoprecipitated from whole cell extracts and used in kinase reactions. This system has been developed taking advantage of the kinase-Glo reagent (Promega), based on ATP depletion technology, but with a wider range of applications. The original aim of the commercial kit is the evaluation of kinase activity of highly purified enzymes, while this system enabled the evaluation of native kinases, retrieved by immunoprecipitation. This method was highly homogeneous and did not require any kind of separation or purification as well. Moreover, it was suitable for basic research and may be useful for low-medium throughput pharmaceutical screening of chemical libraries.

Electrochemical determination of γ-glutamyl transpeptidase activity and its application to a miniaturized analysis system

A novel method to determine the activity of gamma-glutamyl transpeptidase (gamma-GTP) was developed. gamma-l-glutamyl-l-glutamate and glycyl-glycine were used as the substrates for gamma-GTP. l-glutamate produced by the enzymatic reaction was measured with an amperometric l-glutamate sensor. Following the mixing of the substrate solution and a sample solution, the current generated on the l-glutamate sensor continued to increase at a constant rate. The method was used to construct a miniaturized analysis system for the determination of gamma-GTP activity. The system consisted of the l-glutamate sensor formed on a glass substrate and a polydimethylsiloxane (PDMS) flow channel. Since the l-glutamate concentration in the solution increased as the solution was mobilized through the flow channel, a constant current increase was observed. The relation between the slope of the response curve and the activity of gamma-GTP was linear between 35 U l(-1) and 659 U l(-1). The rate analysis in the micro flow channel minimized the influence of interferents. The reproducibility of the output of the micro system was found to be good with a relative standard deviation (R.S.D.) of 5.6% at 659 U l(-1). The activities of gamma-GTP in human serum samples were also determined and compared with values obtained with a conventional spectroscopic method. The values obtained by the two methods were consistent with a correlation coefficient of 0.953.

Clinical analysis by microchip capillary electrophoresis

Clinical analysis often requires rapid, automated, and high-throughput analytical systems. Microchip capillary electrophoresis (CE) has the potential to achieve very rapid analysis (typically seconds), easy integration of multiple analytical steps, and parallel operation. Although it is currently still in an early stage of development, there are already many reports in the literature describing the applications of microchip CE in clinical analysis. At the same time, more fully automated and higher throughput commercial instruments for microchip CE are becoming available and are expected to further enhance the development of applications of microchip CE in routine clinical testing. To put into perspective its potential, we briefly compare microchip CE with conventional CE and review developments in this technique that may be useful in diagnosis of major diseases.

A microfluidic-based enzymatic assay for bioactivity screening combined with capillary liquid chromatography and mass spectrometry

The design and implementation of a continuous-flow microfluidic assay for the screening of (complex) mixtures for bioactive compounds is described. The microfluidic chip featured two microreactors (1.6 and 2.4 microL) in which an enzyme inhibition and a substrate conversion reaction were performed, respectively. Enzyme inhibition was detected by continuously monitoring the products formed in the enzyme-substrate reaction by electrospray ionization mass spectrometry (ESI-MS). In order to enable the screening of mixtures of compounds, the chip-based assay was coupled on-line to capillary reversed-phase high-performance liquid chromatography (HPLC) with the HPLC column being operated either in isocratic or gradient elution mode. In order to improve the detection limits of the current method, sample preconcentration based on a micro on-line solid-phase extraction column was employed. The use of electrospray MS allowed the simultaneous detection of chemical (MS spectra) and biological parameters (enzyme inhibition) of ligands eluting from the HPLC column. The present system was optimized and validated using the protease cathepsin B as enzyme of choice. Inhibition of cathepsin B is detected by monitoring three product traces, obtained by cleavage of the substrate. The two microreactors provided 32 and 36 s reaction time, respectively, which resulted in sufficient assay dynamics to enable the screening of bioactive compounds. The total flow rate was 4 microL min-1, which a 25-fold decrease was compared with a macro-scale system described earlier. Detection limits of 0.17-2.6 micromol L-1 were obtained for the screening of inhibitors, which is comparable to either microtiter plate assays or continuous-flow assays described in the literature.

Quantitative analysis of shape-specific interactions of Rev response element with a positively charged Rev peptide by capillary electrophoresis

Human immunodeficiency virus type 1 (HIV-1) Rev protein is known to regulate the expression of proteins via binding to an RNA site termed the HIV Rev response element (RRE) presumably with a defined shape, mediated mainly by electrostatic interactions. We have developed a quantitative method based on CE-LIF detection for a systematic evaluation of interactions between a truncated RRE (tRRE) RNA and an HIV-1 Rev peptide. Employing a fluorescently labeled HIV-1 Rev protein fragment (RevF) as a probe, buffers were evaluated for the separation and detection as well as for the RNA shape-specific formation of the complex. Selection of an optimal buffer condition allowed us to perform quantitation of the tRRE-RevF complex formation and determine its dissociation constant. In addition, competitive inhibitions of the RNA-peptide interaction by some aminoglycosides were evaluated quantitatively by monitoring the complex peak, resulting in determination of IC(50) values. This sensitive and reliable CE-LIF-based method would be of interest in developing various screening systems for RNA interference in drug discovery.

Fluorometric TLC assay for evaluation of protein kinase inhibitors

A fluorometric assay for measuring protein kinase activity has been developed. The assay is based on the separation of fluorescently marked substrate 5-carboxytetramethylrhodamine-kemptide (5-TAMRA-kemptide) from its phosphorylated counterpart by TLC and quantification of the product ratiometrically by fluorescence imaging. The utility of the assay was demonstrated by measuring the activity of cAMP-dependent protein kinase. 5-TAMRA-kemptide was characterized as a substrate of this kinase by the kinetic parameters K(m)(app) and V(max). The attachment of 5-TAMRA dye to the N terminal of kemptide decreased the K(m)(app) value but did not have a significant effect on the rate and stoichiometry of the phosphorylation reaction. The inhibitory potency of three known inhibitors was evaluated with the new assay. The closeness of the obtained inhibitory activities of the compounds to the activities determined with the phosphocellulose paper-binding assay, as well as the Z' factor value of 0.5, demonstrates the reliability of the new assay for evaluation of inhibitors of protein kinases.

Agonist-induced calcium response in single human platelets assayed in a microfluidic device

To facilitate drug discovery directed toward platelet-specific targets, we developed a platelet isolation and fluorophore-loading method that yields functionally responsive platelets in which we were able to detect agonist-induced calcium flux using a microfluidics-based screening platform. The platelet preparation protocol was designed to minimize preparation-induced platelet activation and to optimize signal strength. Measurement of platelet activation, as monitored by ratiometric determination of agonist-induced calcium flux in fluor-loaded human platelets, was optimized in a macrosample cuvette format in preparation for detection in a microfluidic chip-based assay. For the microfluidic device used in these studies, a cell density of 1 to 2 x 10(6) platelets per milliliter and a nominal flow rate of 5 to 10 nl per second provided optimal event resolution of 5 to 20 platelets traversing the detection volume per unit time. Platelets responded in a dose-dependent manner to adenosine diphosphate and protease-activating peptide (PAR) 1 thrombin receptor-activating peptide (TRAP). The work presented here constitutes proof-of-principle experiments demonstrating the enabling application of a microfluidic device to conduct high-throughput signaling studies and drug discovery screening against human platelet targets.

Applications of capillary electrophoresis on microchip

CE on microchip is an emerging separation technique that has attracted wide attention and gained considerable popularity. Because of miniaturization of the separation format, CE on chip typically offers shorter analysis time and lower reagent consumption with potential development of portable analytical instrumentation. This review with 143 references is focused on proteins and peptides analysis, DNA separation including fragment sizing, genotyping, mutation detection and sequencing, and also the analysis of low-molecular-weight compounds, namely explosive residues and warfare agents, pharmaceuticals and drugs of abuse, and various small molecules in body fluids.

Protein biochips: A new and versatile platform technology for molecular medicine

The human genome has been sequenced and the challenges of understanding the function of the newly discovered genes have been addressed. High-throughput technologies such as DNA microarrays have been developed for the profiling of gene expression patterns in whole organisms or tissues. Protein arrays are emerging to follow DNA chips as possible screening tools. Here, we review the generation and application of microarray technology to obtain more information on the regulation of proteins, their biochemical functions and their potential interaction partners. Already, a large variety of assays based on antibody-antigen interactions exists. In addition, the medical relevance of protein arrays will be discussed.