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

Isolation of High-Molecular-Weight DNA for Long-Read Sequencing Using a High-Salt Gel Electroelution Trap

Long-read sequencing technologies require high-molecular-weight (HMW) DNA of sufficient purity and integrity, which can be difficult to obtain from complex biological samples. We propose a method for purifying HMW DNA that takes advantage of the fact that DNA's electrophoretic mobility decreases in a high-ionic-strength environment. The method begins with the separation of HMW DNA from various impurities by electrophoresis in an agarose gel-filled channel. After sufficient separation, a high-salt gel block is placed ahead of the DNA band of interest, leaving a gap between the separating gel and the high-salt gel that serves as a reservoir for sample collection. The DNA is then electroeluted from the separating gel into the reservoir, where its migration slows due to electrostatic shielding of the DNA's negative charge by excess counterions from the high-salt gel. As a result, the reservoir accumulates HMW DNA of high purity and integrity, which can be easily collected and used for long-read sequencing and other demanding applications without additional desalting. The method is simple and inexpensive, yields sequencing-grade HMW DNA even from difficult plant and soil samples, and has the potential for automation and scalability.

Managing ethylenediaminetetraacetic acid (EDTA) interference in EDTA contaminated samples - selectivity in reporting analytes

BACKGROUND

The widely accepted practice of not reporting any results from ethylenediaminetetraacetic acid (EDTA) contaminated samples necessitates repeat phlebotomy and could delay clinical management decisions. EDTA, however, interferes variably or not at all in assays. EDTA concentration in contaminated samples, like serum indices, therefore, could be used to selectively report the result of analytes not affected at measured EDTA concentration.

METHODS

A serum pool, level 1 and level 3 internal quality control materials were spiked with tripotassium-EDTA to create samples with EDTA concentration up to 6.0 mmol/L. EDTA and 45 common and critically important analytes were measured on Abbott Architect to identify EDTA concentrations for analytes where the change in concentration exceeded their respective reference change value (RCV) for unidirectional change at 95% probability.

RESULTS

Serum potassium increased and calcium decreased exceeding RCV at 0.17 mmol/L EDTA. Alkaline phosphatase (ALP) decreased exceeding RCV at EDTA >1.86 mmol/L. The decrease in iron did not exceed a wide RCV of 61.9% until maximum spiked EDTA but exceeded the desirable specification for allowable total error (30.7%) at EDTA >1.86 mmol/L. The small decrease in magnesium did not exceed RCV. EDTA up to the concentration in blood collection tubes did not affect the results of any other measured analyte.

CONCLUSIONS

Only serum potassium, calcium, ALP and iron studies, of the 45 analytes studied, should not be reported in EDTA contaminated samples. EDTA concentration cut-offs for selective reporting would further facilitate reporting of these analytes in EDTA contaminated samples.

In situ reaction-based ratiometric fluorescent assay for alkaline phosphatase activity and bioimaging

Alkaline phosphatase (ALP) is an important biomarker, it is of great significance to develop a sensitive and efficient analytical method for ALP. In this study, an in situ reaction based ratiometric fluorescence assay for ALP was proposed. l-ascorbic acid-2-phosphate (AA2P) was used as a substrate for ALP, and Cu²⁺/o-phenylenediamine (OPD) were involved in this system. Cu²⁺ can oxidize OPD to 2,3-diaminophenazine (OPDox) with an emission centered at 566 nm. The presence of ALP can catalyze the hydrolysis of AA2P to ascorbic acid (AA), which will inhibit the production of OPDox and reduce the corresponding fluorescence intensity, and AA will react with OPD to generate 3-(dihydroxyethyl)furan[3,4-b]quinoxalin-1-one (DFQ) with an emission peak at 447 nm. The fluorescence ratio of F447/F566 has a linear relationship with ALP activity. The proposed method is highly sensitive, finely selective, cost efficiency and easy to operate, it exhibits good linearity in the range of 0.5-22 and 22-40 mU·mL^-1, with a detection limit as low as 0.06 mU·mL^-1. The excellent applicability of this strategy in human serum samples and MCF-7 cells imaging suggests that this method has promising prospects for biomedical research.

Development of a Selective Assay of Tyrosine and Its Producing and Metabolizing Enzymes Utilizing Pulse-UV Irradiation-Induced Chemiluminescence

A new pulse UV irradiation-induced chemiluminescence (CL) determination method was developed for l-tyrosine using the luminol derivative L-012. The proposed method depends on the formation of reactive oxygen species (ROS) upon pulse UV irradiation of l-tyrosine; then, these ROS react with L-012 producing strong CL. The proposed method showed excellent sensitivity and ultraselectivity toward l-tyrosine. The mechanism of the developed CL method was studied using ROS scavengers, HPLC, and mass spectrometry. The method was linear for l-tyrosine in the range of 0.03-50 μM. Minor changes in the l-tyrosine structure, including hydroxylation, dehydroxylation, phosphorylation, or decarboxylation, were found to lead to a strong decrease in CL. Using the excellent selectivity of the proposed method for l-tyrosine, we have developed a CL assay for measuring alkaline phosphatase activity in the range of 0.02-15 U/L with the limit of detection (LOD) of 4 mU/L using the nonchemiluminescent O-phospho-l-tyrosine as a substrate. Furthermore, the CL reaction was applied for tyrosinase activity assay as this enzyme can convert l-tyrosine to the nonchemiluminescent l-dopa. The decrease in CL is correlated with the tyrosinase activity in the range of 0.025-0.75 U/mL with an LOD of 1.5 mU/mL. Moreover, the tyrosinase activity assay was successfully applied for the determination of IC₅₀ of the tyrosinase inhibitors kojic acid and benzoic acid. Therefore, our novel pulse UV irradiation CL method for the determination of l-tyrosine was not only suitable for the determination of this vital amino acid but also extended to the successful determination of its producing and metabolizing enzymes and their inhibitors.

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.

Aggregation-induced emission of luminol: a novel strategy for fluorescence ratiometric detection of ALP and As(v) with high sensitivity and selectivity

Luminol is introduced as a ligand for Tb³⁺ which, combined with GMP, leads to a sensor which is more robust, sensitive, and efficient.

A self-directed and reconstructible immobilization strategy: DNA directed immobilization of alkaline phosphatase for enzyme inhibition assays

A DNA-directed immobilization technique is used to develop a common method for the reversible and self-directed immobilization of enzymes.

Enzyme molecules in solitary confinement

Large arrays of homogeneous microwells each defining a femtoliter volume are a versatile platform for monitoring the substrate turnover of many individual enzyme molecules in parallel. The high degree of parallelization enables the analysis of a statistically representative enzyme population. Enclosing individual enzyme molecules in microwells does not require any surface immobilization step and enables the kinetic investigation of enzymes free in solution. This review describes various microwell array formats and explores their applications for the detection and investigation of single enzyme molecules. The development of new fabrication techniques and sensitive detection methods drives the field of single molecule enzymology. Here, we introduce recent progress in single enzyme molecule analysis in microwell arrays and discuss the challenges and opportunities.

Screening of neuraminidase inhibitors from traditional Chinese medicine by transverse diffusion mediated capillary microanalysis

A transverse diffusion mediated capillary microanalysis method has been developed for screening of neuraminidase inhibitors from traditional Chinese medicine. The enzyme, substrate and inhibitors were sequentially injected, mixed efficiently by transverse diffusion of laminar flow profiles, then incubated and separated in the same capillary. To enhance the mixing efficiency of reactants, running buffer was injected by alternately applying +5 kPa and -5 kPa at the capillary inlet and the procedure was repeated three times. The capillary electrophoresis (CE) separation conditions and reactants mixing conditions were optimized. Dual-wavelength detection was employed to eliminate the interference with natural compounds. The method has been applied to determine the kinetics constant of neuraminidase and screen 12 compounds from traditional Chinese medicine. Four compounds have been found to be positive for enzyme inhibition. The results are in good agreement with those reported in the literature. The method realized the mixing of substrate and enzyme with identical electrophoretic mobility. This novel CE method was simple, rapid, economic, and fully automated. Therefore, it was appropriate for neuraminidase inhibitors screening and could be extended to other high-throughput screening of active components from traditional Chinese medicine.

Large-volume sample stacking with polarity switching for monitoring of nucleotide pyrophosphatase/phosphodiesterase 1 (NPP1) reactions by capillary electrophoresis

Nucleotide pyrophosphatase/phosphodiesterase 1 (NPP1) is a membrane glycoprotein involved in the hydrolysis of extracellular nucleotides. Its main substrate is ATP yielding AMP and pyrophosphate. NPP1 has been proposed as a novel drug target, for diabetes type 2 and the treatment of calcium pyrophosphate dihydrate deposition disease leading to inflammatory arthritis. The monitoring of NPP1 reactions is difficult because its velocity is very slow requiring highly sensitive analytical procedures. In this study, a method of large-volume sample stacking with polarity switching was developed, and separations were optimized. Large sample volumes were loaded by hydrodynamic injection (5 psi, 13 s) followed by removal of a large plug of sample matrix from the capillary using polarity switching (-10 kV). The stacked analytes were subsequently separated in phosphate buffer (100 mM, pH 9.2) at 20 kV. The validated method was found to be linear (R(2) = 0.9927) in the concentration range of 0.05-50 μM of AMP, with high accuracy and precision. The determined LOD and LOQ of AMP were 18 nM and 60 nM, respectively. Compared to a previously reported CE procedure using sweeping technique, a fivefold improvement of sensitivity was achieved. Moreover, the new technique was faster, and reproducibility of migration times was improved (RSD value = 1.2%). Importantly, adenine nucleotide analogs and derivatives tested as NPP1 inhibitors could be completely separated from the substrate ATP and the enzymatic product AMP. The method was applied to NPP1 inhibition assays investigating nucleotide-derived inhibitors in the presence of ATP.

Dual detection of cancer biomarker CA125 using absorbance and electrochemical methods

An enzyme-linked immunoassay based on dual signal transduction mechanisms has been developed for detection of ovarian cancer biomarker CA125. The immunoassay uses a nanoelectrode array (NEA) chip and absorbance methods for the dual detection. The NEA is used to confirm the optical detection of CA125 that is carried out in a high-binding 96-well plate. An alkaline phosphatase (AP) enzyme was used to label the detection antibody to allow for both the optical and electrochemical detection of CA125. Two kinds of substrates were catalyzed by the AP enzyme. para-Nitrophenylphosphate (PNPP) produces chromogenic para-nitrophenol (PNP), which can be optically detected at 405 nm. para-Aminophenylphosphate (PAPP) produces electroactive para-aminophenol (PAP), which can be detected amperometrically between -0.1 and 0.3 V. The linear ranges have been determined to be 5-1000 U mL(-1) and 5-1000 U mL(-1) for the optical and electrochemical immunoassays, respectively. The limit of detection of the optical immunoassay is 1.3 U mL(-1) and 40 U mL(-1) for the optical and electrochemical methods, respectively.

Investigation and verification of a bioluminescent biosensor for the quantitation of ara-CTP generation: a biomarker for cytosine arabinoside sensitivity in acute myeloid leukaemia

A novel whole cell bacterial biosensor, which emits light in response to the active metabolite of cytosine arabinoside (ara-C, cytarabine), ara-CTP, has been investigated and verified. The biosensor has been formulated as an ex vivo assay, designed for peripheral blood or bone marrow cells, which can produce a clinical result within a working day. The nucleoside analogue ara-C is a key agent for treatment of acute myeloid leukaemia (AML); treatment decisions are made rapidly with AML, patients often receiving same-day commencement of chemotherapy. Currently no rapid predictive test is available to select appropriate therapy for patients prior to treatment. Experiments were designed to determine optimal assay conditions using leukaemic cell lines. We observed a significant increase (~15 fold) in bioluminescence signal compared to control after 8-h incubation of the biosensor with ara-C. This corresponded to a >2-log increase in light output per bacterial cell. Interestingly, bioluminescence conferred a survival advantage to the bacteria following ara-C treatment. The assay is sensitive (lower limit of quantitation of 0.05 µM), selective, accurate (≤ 15% RE) and precise (≤ 15% coefficient of variation) over a linear concentration range of ara-CTP (0.05-0.5 µM), and detection is independent of reaction volume. Recovery of added standard was tested using ex vivo patient leukaemic cells (n=5). Stability studies on lyophilized bacterial biosensor were performed to ensure maintenance of performance over 12 months. The biosensor assay could be invaluable to the clinician, assisting with treatment selection, and potentially mitigating the risks of resistance and toxicity observed with this drug.

Graphene oxide-based fluorescent "on/off" switch for visual bioassay using "molecular beacon"-hosted Hoechst dyes

In this study, the fluorescence of Hoechst dyes is significantly lit up by addition of our designed MB probe, forming a complex of "molecular beacon"-hosted Hoechst dyes (HMB). Combined with this property, a novel graphene oxide (GO)-based fluorescent "on/off" switch was developed to visually follow bioassay utilizing HMB as signal indicators and GO as an excellent energy acceptor to efficiently quench the fluorescence of HMB in a label-easy format. We have demonstrated its application for label-easy fluorescence "turn on" detection of sequence-specific DNA and "turn off" detection of exonuclease with sensitivity and selectivity in a single step in homogeneous solution. Compared to traditional molecular beacons, the proposed design is cost-effective and simple to prepare without fluorescence labeling or chemical modification.

Sit4p/PP6 regulates ER-to-Golgi traffic by controlling the dephosphorylation of COPII coat subunits

Previous studies show that the COPII coat is phosphorylated. The phosphorylated coat, however, cannot rebind to the ER to initiate a new round of vesicle budding. The present study shows that Sit4p/PP6, a Ser/Thr phosphatase, dephosphorylates the COPII coat. Consistent with a role in coat recycling, Sit4p/PP6 regulates ER-to-Golgi traffic.

Traffic from the endoplasmic reticulum (ER) to the Golgi complex is initiated when the activated form of the GTPase Sar1p recruits the Sec23p-Sec24p complex to ER membranes. The Sec23p-Sec24p complex, which forms the inner shell of the COPII coat, sorts cargo into ER-derived vesicles. The coat inner shell recruits the Sec13p-Sec31p complex, leading to coat polymerization and vesicle budding. Recent studies revealed that the Sec23p subunit sequentially interacts with three different binding partners to direct a COPII vesicle to the Golgi. One of these binding partners is the serine/threonine kinase Hrr25p. Hrr25p phosphorylates the COPII coat, driving the membrane-bound pool into the cytosol. The phosphorylated coat cannot rebind to the ER to initiate a new round of vesicle budding unless it is dephosphorylated. Here we screen all known protein phosphatases in yeast to identify one whose loss of function alters the cellular distribution of COPII coat subunits. This screen identifies the PP2A-like phosphatase Sit4p as a regulator of COPII coat dephosphorylation. Hyperphosphorylated coat subunits accumulate in the sit4Δ mutant in vivo. In vitro, Sit4p dephosphorylates COPII coat subunits. Consistent with a role in coat recycling, Sit4p and its mammalian orthologue, PP6, regulate traffic from the ER to the Golgi complex.

New development in in-capillary electrophoresis techniques for kinetic and inhibition study of enzymes

Enzymes are often quantified by measuring their biological activity. Capillary electrophoresis is gaining its position in this field due to the ongoing trend to miniaturize biochemical assays. The aim of this work was to compare pre-capillary (off-line) and in-capillary electrophoresis techniques for studying enzymatic activity. The β-galactosidase (β-Gal) was chosen as a model enzyme. Each technique was optimized independently in order to decrease analyte consumption (to few tens of nanoliters), incubation time (to few seconds) and analysis time (below 1 min). Several experimental parameters (ionic strength of the background electrolyte (BGE) and of the incubation buffer, incubation time, injected volumes, …) were optimized by following peak efficiencies, resolution and repeatability. To monitor the performance of each technique, the catalytic constants (V(max) and K(m)) of 4-nitro-phenyl-d-galactopyranoside (PNPG) hydrolysis by β-Gal as well as the inhibition constants (K(i) and IC(50)) by a competitive inhibitor 2-nitrophenyl-1-thio-β-d-thiogalactopyranoside (ONPTG) were determined. The results obtained were cross compared and were also evaluated by comparison to a standard spectrophotometric method. EMMA proved to be the best technique in terms of sample consumption and speed. The short-end injection was successfully used which speeded-up electrophoretic analysis (<0.8 min). It is a very powerful tool for studying enzymatic inhibition. Usually, the inhibitor is injected in the capillary mixed to the substrate especially when both have similar mobilities. We show in this work, for the first time, that combining at-inlet reaction with EMMA-CE allows enzyme inhibition to be realized without any prior mixing of the substrate and the inhibitor. This approach is very interesting for screening inhibitors, rapidly and without excessive substrate consumption.

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.

Determination of total antioxidant capacity of commercial beverage samples by capillary electrophoresis via inline reaction with 2,6-dichlorophenolindophenol

This paper demonstrates proof-of-concept for the use of electrophoretically mediated microanalysis (EMMA) as a new approach to the determination of total antioxidant capacity (TAC). EMMA is a low-volume, high-efficiency capillary electrophoretic technique that has to date been underutilized for small molecule reactions. Here, nanoliter volumes of 2,6-dichlorophenolindophenol (DCIP) reagent solution are mixed with an antioxidant-containing sample within the confines of a narrow-bore capillary tube. The mixing is accomplished by exploiting differential migration rates of the reagents when a voltage field is applied across the length of the capillary tube. The ensuing electron transfer reaction between DCIP and the antioxidant(s) is then used as a quantitative measure of the TAC of the sample. Linear calibration using either redox form of DCIP is accomplished with standard solutions of ascorbic acid. Several commercial beverage samples are analyzed, and the TAC values obtained with the reported methodology are compared to results obtained with the widely used ferric reducing antioxidant power (FRAP) spectroscopic method. For the analysis of real samples of unknown ionic strength, the method of standard additions is shown to be superior to the use of external calibration. This easily automated EMMA method may represent a useful new approach to TAC determination.

Differential mitotic activation of endogenous c-Src, c-Yes, and Lyn in HeLa cells

Src-family tyrosine kinases (SFKs) play an important role in mitosis. Despite overlapping expression of multiple SFK members, little is known about how individual SFK members are activated in M phase. Here, we examined mitotic activation of endogenous c-Src, c-Yes, and Lyn, which are co-expressed in HeLa cells. c-Src, c-Yes, and Lyn were activated at different levels in M phase, and the activation was inhibited by Cdc2 inactivation. Mitotic c-Src and c-Yes exhibited normal- and retarded-electrophoretic-mobility forms on SDS-polyacrylamide gels, whereas Lyn did not show mobility retardation. Like c-Src, the retardation of electrophoretic mobility of c-Yes was caused by Cdc2-mediated phosphorylation. The normal- and retarded-mobility forms of c-Src were comparably activated, but activation of the retarded-mobility form of c-Yes was higher than that of the normal-mobility form of c-Yes. Thus, these results suggest that endogenous c-Src, c-Yes, and Lyn are differentially activated through Cdc2 activation during M phase.

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.

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.

Development and validation of a capillary electrophoresis method for the characterization of herpes simplex virus type 1 (HSV-1) thymidine kinase substrates and inhibitors

A fast, convenient capillary electrophoresis (CE) method was developed for monitoring the enzymatic reaction of herpes simplex virus type 1 thymidine kinase (HSV-1 TK). The reaction was performed in a test tube followed by quantitative analysis of the products. The optimized CE conditions were as follows: polyacrylamide-coated capillary (20 cm effective length x 50 microm), electrokinetic injection for 30s, 50 mM phosphate buffer at pH 6.5, constant current of -60 microA, UV detection at 210 nm, UMP or cAMP were used as internal standards. Phosphorylated products eluted within less than 7 min. The limits of detection were 0.36 microM for dTMP and 0.86 microM for GMP. The method was used to study enzyme kinetics, and to investigate alternative substrates and inhibitors.

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.

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.

A heat inducible tyrosinase with distinct properties from Bacillus thuringiensis

AIMS

The objective of this work was to purify the tyrosinase from Bacillusthuringiensis subsp. kurstaki (Bt) (CCTCC AB 90010) and study its enzymatic properties.

METHODS AND RESULTS

A 'one-step' purification method was used in this work, which was an easy, high-yield purification method. Tyrosinase activity of this purity was measured under different conditions to study its kinetic characterizations. The optimum pH and thermal stability of this enzyme were also determined. The results revealed that the tyrosinase from Bt has distinct properties compared with those from other sources.

CONCLUSIONS

A heat-inducible tyrosinase of a wild strain of Bt was identified and partially characterized.

SIGNIFICANCE AND IMPACT OF THE STUDY

The distinct properties of Bt tyrosinase are important to the application of Bt as a biology pesticide.