UDP-glucose dehydrogenase supports autophagy-deficient PDAC growth via increasing hyaluronic acid biosynthesis

Autophagy is an essential degradation and recycling process that maintains cellular homeostasis during stress or nutrient deprivation. However, certain types of tumors such as pancreatic cancers can circumvent autophagy inhibition to sustain growth. The mechanism that autophagy-deficient pancreatic ductal adenocarcinoma (PDAC) uses to grow under nutrient deprivation is poorly understood. Our data show that nutrient deprivation in PDAC results in UDP-glucose dehydrogenase (UGDH) degradation, which is dependent on autophagic cargo receptor sequestosome 1 (p62). Moreover, we demonstrate that accumulated UGDH is indispensable for autophagy-deficient PDAC cells proliferation by promoting hyaluronic acid (HA) synthesis upon energy deprivation. Using an orthotopic mouse model of PDAC, we find that inhibition of HA synthesis by targeting UGDH in PDAC reduces tumor weight. Thus, the combined inhibition of HA and autophagy might be an attractive strategy for PDAC treatment.

UDP-glucose dehydrogenase (UGDH) in clinical oncology and cancer biology

UDP-glucose-6-dehydrogenase (UGDH) is a cytosolic, hexameric enzyme that converts UDP-glucose to UDP-glucuronic acid (UDP-GlcUA), a key reaction in hormone and xenobiotic metabolism and in the production of extracellular matrix precursors. In this review, we classify UGDH as a molecular indicator of tumor progression in multiple cancer types, describe its involvement in key canonical cancer signaling pathways, and identify methods to inhibit UGDH, its substrates, and its downstream products. As such, we position UGDH as an enzyme to be exploited as a potential prognostication marker in oncology and a therapeutic target in cancer biology.

Development of a novel ultrasound- and biocrosslinking-enhanced immobilization strategy with application to food enzymes

The increasing demand for greener food production makes biocatalysts more desirable than traditional production approaches. One limiting factor for biocatalyst efficiency is the immobilization strategy. In this work, a novel immobilization method was developed with the tyrosine-tag crosslinking mechanism. The immobilization efficiency was further enhanced with ultrasound treatment. Such a strategy was proven to be efficient with food enzyme lipase, d-amino acid oxidase and glucose dehydrogenase when they were immobilized on macroporous resins, amino resins, epoxy resins, and multiwalled carbon nanotubes. For lipase, glucose dehydrogenase and d-amino acid oxidase, the immobilization yield on macroporous resins increased by 20.4%, 21.1% and 24.1%, respectively. In addition, the immobilized enzymes had enhanced reusability, with a high degree of activity (more than 85%) detected after six cycles. Furthermore, the enzyme electrochemical sensors constructed by enzyme crosslinking have higher sensitivity, with peak currents 4-8 times those of sensors with uncrosslinked enzymes. The enzyme immobilization strategy developed in this study paves the way for better application of biocatalysts in the food industry.

Identification of a lactose-oxidizing enzyme in Escherichia coli and improvement of lactobionic acid production by recombinant expression of a quinoprotein glucose dehydrogenase from Pseudomonas taetrolens

Lactobionic acid (LBA), an aldonic acid prepared by oxidation of the free aldehyde group of lactose, has been broadly used in cosmetic, food, and pharmaceutical industries. Although Escherichia coli is unable to produce LBA naturally, a wild-type E. coli strain successfully produced LBA from lactose upon pyrroloquinoline quinone (PQQ) supplementation, indicating that E. coli contains at least one lactose-oxidizing enzyme as an apo-form. By inactivating the candidate genes in the E. coli chromosome, we found that the lactose-oxidizing enzyme of E. coli was the quinoprotein glucose dehydrogenase (GCD). To improve the LBA production ability of the E. coli strain, quinoprotein glucose dehydrogenase (GDH) from Pseudomonas taetrolens was recombinantly expressed and culture conditions such as growth temperature, initial lactose concentration, PQQ concentration, and isopropyl-β-D-1-thiogalactopyranoside induction concentration were optimized. We performed batch fermentation using a 5-L bioreactor under the optimized culture conditions determined in flask culture experiments. After batch fermentation, the LBA production titer, yield, and productivity of the recombinant E. coli strain were 200 g/L, 100 %, and 1.28 g/L/h, respectively. To the best our knowledge, this is the first report to identify the lactose-oxidizing enzyme of E. coli and to produce LBA using a recombinant E. coli strain as the production host. Because E. coli is one of the most easily genetically manipulated bacteria, our result provides the groundwork to further enhance LBA production by metabolic engineering of LBA-producing E. coli.

Mediator Preference of Two Different FAD-Dependent Glucose Dehydrogenases Employed in Disposable Enzyme Glucose Sensors

Most commercially available electrochemical enzyme sensor strips for the measurement of blood glucose use an artificial electron mediator to transfer electrons from the active side of the enzyme to the electrode. One mediator recently gaining attention for commercial sensor strips is hexaammineruthenium(III) chloride. In this study, we investigate and compare the preference of enzyme electrodes with two different FAD-dependent glucose dehydrogenases (FADGDHs) for the mediators hexaammineruthenium(III) chloride, potassium ferricyanide (the most common mediator in commercial sensor strips), and methoxy phenazine methosulfate (mPMS). One FADGDH is a monomeric fungal enzyme, and the other a hetero-trimeric bacterial enzyme. With the latter, which contains a heme-subunit facilitating the electron transfer, similar response currents are obtained with hexaammineruthenium(III), ferricyanide, and mPMS (6.8 µA, 7.5 µA, and 6.4 µA, respectively, for 10 mM glucose). With the fungal FADGDH, similar response currents are obtained with the negatively charged ferricyanide and the uncharged mPMS (5.9 µA and 6.7 µA, respectively, for 10 mM glucose), however, no response current is obtained with hexaammineruthenium(III), which has a strong positive charge. These results show that access of even very small mediators with strong charges to a buried active center can be almost completely blocked by the protein.

Maltose interference-free test strips for blood glucose testing at point-of-care: a laboratory performance evaluation

BACKGROUND

Maltose interference is a concern with blood glucose testing at point-of-care. We evaluated a maltose interference-free test strip (with a modified recombinant glucose dehydrogenase-pyrroloquinoline quinone system) for the Accu-Chek(®) Performa glucose meter (Roche Diagnostics, Mannheim, Germany).

METHODS

Blood specimens (n = 120) sent for clinical laboratory glucose testing were used in assessing performance characteristics, including imprecision, linearity, clinical impact analysis, and method comparison, of the test strips. To evaluate sugar interference, two heparinized blood specimens were spiked with maltose, xylose, and galactose (up to 500 mg/dL) followed by testing with modified Performa, Accutrend(®) (Roche Diagnostics), and Advantage II (Roche Diagnostics) test strips and by the laboratory method.

RESULTS

Test strips demonstrated total laboratory coefficients of variation of <7%; within-run coefficients of variation were 2.7-5.4% for blood glucose at 2.5-19.7 mmol/L. Clarke Error Grid analysis of the 120 results (0.8-27.6 mmol/L) showed all values to be within critical clinical limits. Comparison with laboratory results gave 0.960 correlation (Spearman's r(2)) with a Deming regression y (Performa) = 0.95x (laboratory) - 0.11 mmol/L (SEy|x0.06 mmol/L). A slight negative bias (-0.5 mmol/L) was demonstrated with the Bland-Altman difference plot. Maltose (up to 13.9 mmol/L) and xylose (33.3 mmol/L) had no effect, but galactose (2.2 mmol/L) showed interference. The sugars also affected test strips for Advantage II but not Accutrend glucose meters. With International Organization for Standardization ISO 15197:2003 criteria, 99% of the 120 results determined by the test strips were within the minimal acceptable performance; only one of 106 (5.9 mmol/L) was >20% from the laboratory result.

CONCLUSIONS

The modified and improved Performa test strips were not affected by maltose and xylose. They meet ISO 15197:2003 requirements with a slight bias (-0.5 mmol/L) compared to the laboratory method.

Continuous asymmetric ketone reduction processes with recombinant Escherichia coli

The reduction of methyl acetoacetate was carried out in continuously operated biotransformation processes catalyzed by recombinant Escherichia coli cells expressing an alcohol dehydrogenase from Lactobacillus brevis. Three different cell types were applied as biocatalysts in three different cofactor regeneration approaches. Both processes with enzyme-coupled cofactor regeneration catalyzed by formate dehydrogenase or glucose dehydrogenase are characterized by a rapid deactivation of the biocatalyst. By contrast the processes with substrate-coupled cofactor regeneration by alcohol dehydrogenase catalyzed oxidation of 2-propanol could be run over a period of 7 weeks with exceedingly high substrate and cosubstrate concentrations of up to 2.5 and 2.8 mol L(-1), respectively. Even under these extreme conditions, the applied biocatalyst showed a good stability with only marginal leakage of intracellular cofactors.

GDH biosensor based off-line capillary immunoassay for alkylphenols and their ethoxylates

The application of a quinoprotein glucose dehydrogenase modified thick-film sensor as label detector in a capillary immunoassay (CIA) for xenoestrogens is presented. The detection of the alkylphenols and their ethoxylates is based on the competition between the analyte and tracer molecules for the binding sites of anti-alkylphenol ethoxylate antibodies. This assay is performed off-line in small disposable PVC capillaries coated with immobilized antibodies. This format allows the combination of the assay with a small portable device potentially useful for on-site environmental monitoring. Beside high amplification the utilization of beta-galactosidase as enzyme label allows the direct combination with a GDH biosensor at optimal pH conditions. The bioelectrocatalytic properties of this biosensor offer an additional amplification and thus allow a very sensitive quantification of 4-aminophenol, generated by the beta-galactosidase. Detection limits of the analytes in the microg/l range were obtained, while other phenolics and surfactants showed no or very little cross reactivity.

Continuous production of high-content fructooligosaccharides by a complex cell system

A complex biocatalyst system with a bioreactor equipped with a microfiltration (MF) module was employed to produce high-content fructooligosaccharides (FOS) in a continuous process initiated by a batch process. The system used mycelia of Aspergillus japonicus CCRC 93007 or Aureobasidium pullulans ATCC 9348 with beta-fructofuranosidase activity and Gluconobacter oxydans ATCC 23771 with glucose dehydrogenase activity. Calcium carbonate slurry was used to control pH to 5.5, and gluconic acid in the reaction mixture was precipitated as calcium gluconate. Sucrose solution with an optimum concentration of 30% (w/v) was employed as feed for the complex cell system, and high-content FOS was discharged continuously from a MF module. The complex cell system was run at 30 degrees C with an aeration rate of 5 vvm and produced more than 80% FOS with the remainder being 5-7% glucose and 8-10% sucrose on a dry weight basis, plus a small amount of calcium gluconate. The system worked for a 7-day continuous production process with a dilution rate of 0.04 h(-1), and the volumetric productivity for total FOS was more than 160 g L(-1) h(-1).

A glucose dehydrogenase biosensor as an additional signal amplification step in an enzyme-flow immunoassay

Both the antibody affinity and the detectability of the label are essential in deciding the final characteristics of a heterogeneous immunoassay. This paper describes an approach to obtain a supplementary enhancement of the signal generated by using an enzyme label, e.g., by including the product of the enzymatic reaction in an additional amplification cycle during the detection step performed with an amperometric biosensor based on glucose dehydrogenase (GDH). An immunoassay format with a labelled analyte derivative that competes with the analyte present in the sample for a limited amount of antibody binding sites was employed. The beta-galactosidase label hydrolyses the substrate aminophenyl-beta-galactopyranoside, and the generated aminophenol enters then into a bioelectrocatalytic amplification cycle at the GDH biosensor. The principle was applied for determination of 4-nitrophenol, with the best minimal concentration of 1.5 microM and a midpoint of the calibration of 24 microM. The potentials and limitations of such a system are discussed.

Electrodes modified with nitrofluorenone derivatives as a basis for new biosensors

We report about the electrocatalytic properties of electrodes modified by adsorption of nitro-fluorenone derivatives. The stable, adherent monolayer of these catalyst precursors can be transformed electrochemically into the corresponding hydroxylamine compounds (R-NO(2)+4e+4H(+)-->R-NHOH+H(2)O). The completely reversible two electron oxidation of the hydroxylamine leads to the nitroso compounds (R-NHOH-->R-NO+2e+2H(+)) that exhibit high catalytic activity in the electrooxidation of NADH at low overpotentials (-30 mV vs. Ag/AgCl) and therefore constitute a new family of efficient redox mediators for biosensor applications. A significant increase in catalytic activity (up to 500%) is observed after addition of calcium ions to the electrolyte. This is explained by a specific and bridging complexation between the coenzyme's phosphate groups and a carboxyl group present in the catalyst molecule. The interaction favours the contact between NADH and the surface confined catalyst, leading to a higher electron transfer efficiency. This interaction can be used in an approach of molecular level design for controlled monolayer deposition of catalyst, Ca(2+), NAD+ and enzyme. A very simple and inexpensive modification scheme, essentially based on electrostatic attraction, leads to electrodes that can be employed as reagentless biosensors for the electrochemical detection of common and commercially interesting analytes like glucose.

Glucose biochip: dual analyte response in connection to two pre-column enzymatic reactions

This article describes a novel 'Lab-on-a-Chip' protocol generating two electrophoretic peaks for a single analyte, based on the coupling of two different pre-column enzymatic reactions of the same substrate followed by electrophoretic separation of the reaction products. Such operation is illustrated for the measurement of glucose in connection to the corresponding glucose oxidase (GOx) and glucose dehydrogenase (GDH) reactions. The pre-column enzymatic reactions generate hydrogen peroxide and NADH species, that are separated (based on their different charges) and detected at the end-column amperometric detector. The peak current ratio can be used for confirming the peak identity, estimating the peak purity, addressing co-migrating interferences, and deviations from linearity. A driving voltage of 2000 V results in peroxide and NADH migration times of 93 and 260 s, respectively. Factors influencing the unique dual glucose response are examined and optimized. The concept can be extended to different target analytes based on the coupling of two pre-column reactions with electrophoretic separation of the reaction products.

L-ascorbic acid biosynthesis

Biosynthesis of L-ascorbate (vitamin C) occurs by different pathways in plants and mammals. Yeast contain D-erythroascorbate, a C5 analog of ascorbate. UDP-D-glucuronic acid is the precursor in mammals. Loss of UDP forms glucuronic acid/glucuronolactone. Reduction of these at C-1 then forms L-gulonic acid/L-gulono-1,4-lactone. The lactone is oxidized by a microsomal L-gulono-1,4-lactone oxidase to ascorbate. Only the L-gulono-1,4-lactone oxidase has been purified and cloned, and very little is known about the properties of the other enzymes. Plants form ascorbate from GDP-D-mannose via GDP-L-galactose, L-galactose, and L-galactono-1,4-lactone. The final oxidation of L-galactono-1,4-lactone to ascorbate is catalyzed by a mitochondrial L-galactono-1,4-lactone dehydrogenase located on the inner membrane and using cytochrome c as electron acceptor. GDP-mannose pyrophosphorylase and L-galactono-1,4-lactone dehydrogenase have been cloned. Yeast synthesizes D-erythroascorbate from D-arabinose and D-arabinono-1,4-lactone in a pathway analogous to that in plants. The plant, mammalian, and yeast aldonolactone oxidase/dehydrogenases that catalyze the last step in each pathway have significant sequence homology. L-Gulono-1,4-lactone oxidase is mutated and not expressed in animals, such as primates, that have lost ascorbate biosynthesis capacity. Assessment of the literature reveals that little is known about many of the enzymes involved in ascorbate biosynthesis or about the factors controlling flux through the pathways. There is also a possibility that minor alternative pathways exist in plants and mammals.

Enzyme fluorescence as a sensing tool: new perspectives in biotechnology

The technology for fluorescence protein-sensing is advancing rapidly owing to the continued introduction of new concepts, new fluorophores, and proteins engineered for sensing-specific analytes. Concerns about the reversibility and selectivity of engineered proteins are being addressed by developing biosensors that are based on the utilisation of coenzyme-depleted enzymes. Such biomolecules do not consume the substrate and can exhibit conformational changes upon the binding of the analyte, which can be easily detected as fluorescence change. In addition, concerns about the stability of biosensors can be overcome by using thermostable enzymes isolated from thermophilic microorganisms. Finally, the development of new techniques such as polarization-based sensing, anisotropy-based sensing and lifetime-based sensing, all of which can be accomplished with light-emitting diodes as the light source, is prompting the design of a new class of specific and stable biosensors, as has occurred with blood glucose measurement. These biosensors represent a valid alternative to the conventional clinical chemistry diagnostics.

A thermophilic apoglucose dehydrogenase as nonconsuming glucose sensor

Blood glucose is a clinically important analytes for diabetic health care. In this preliminary report we describe a protein biosensor for d-glucose based on a thermostable glucose dehydrogenase. The glucose dehydrogenase was noncovalently labeled with 8-anilino-1-naphthalene sulfonic acid (ANS). The ANS-labeled enzyme displayed an approximate 25% decrease in emission intensity upon binding glucose. This decrease can be used to measure the glucose concentration. Our results suggest that enzymes which use glucose as their substrate can be used as reversible and nonconsuming glucose sensors in the absence of required cofactors. Moreover, the possibility of using inactive apoenzymes for a reversible sensor greatly expands the range of proteins which can be used as sensors, not only for glucose, but for a wide variety of biochemically relevant analytes.

Aerobic sporulating bacteria. I. Glucose dehydrogenase of Bacillus cereus

Bach, John A. (Michigan State University, East Lansing) and H. L. Sadoff. Aerobic sporulating bacteria. I. Glucose dehydrogenase of Bacillus cereus. J. Bacteriol. 83:699-707. 1962.-A heat-resistant glucose dehydrogenase occurs in cultures of Bacillus cereus which are in the initial stages of sporulation. This enzyme is, kinetically, identical to the glucose dehydrogenase which can be extracted from mature spores, but is considerably more heat resistant than the spore-free enzyme. The two enzymes produce identity lines in two-dimensional immunodiffusion experiments, and their behavior in chromatographic and electrophoretic studies is also identical.A labile glucose dehydrogenase can be extracted from germinated spores of B. cereus. It differs from its stable counterparts in possessing a higher pH optimum for enzymatic activity.

Assessment of the state-of-the-art trueness and precision of serum total-calcium and glucose measurements in Finnish laboratories--the QSL-Finland study

The purpose of the QSL-Finland study was to assess the state-of-the-art trueness and precision of serum total-calcium and glucose measurements in Finnish clinical laboratories. For this purpose, 21 hospitals and clinical institutes were selected. They measured six single donation sera, the total-calcium (t-calcium) and glucose content of which had been determined by ion chromatography and isotope dilution-gas chromatography-mass spectrometry (ID-GC-MS) reference methods. The results were interpreted in light of specifications for imprecision, bias and total error of routine methods that have been proposed in the past. The data revealed that the performance of t-calcium and glucose methods is generally acceptable in Finnish clinical laboratories. This study did not lead to a separation of laboratories according to accreditation. In consequence, it seems that accreditation, in its present form, cannot substitute dedicated quality assurance practices.

Multicenter study of oxygen-insensitive handheld glucose point-of-care testing in critical care/hospital/ambulatory patients in the United States and Canada

OBJECTIVES

Existing handheld glucose meters are glucose oxidase (GO)-based. Oxygen side reactions can introduce oxygen dependency, increase potential error, and limit clinical use. Our primary objectives were to: a) introduce a new glucose dehydrogenase (GD)-based electrochemical biosensor for point-of-care testing; b) determine the oxygen-sensitivity of GO- and GD-based electrochemical biosensor test strips; and c) evaluate the clinical performance of the new GD-based glucose meter system in critical care/hospital/ambulatory patients.

DESIGN

Multicenter study sites compared glucose levels determined with GD-based biosensors to glucose levels determined in whole blood with a perchloric acid deproteinization hexokinase reference method. One site also studied GO-based biosensors and venous plasma glucose measured with a chemistry analyzer. Biosensor test strips were used with a handheld glucose monitoring system. Bench and clinical oxygen sensitivity, hematocrit effect, and precision were evaluated.

SETTING

The study was performed at eight U.S. medical centers and one Canadian medical center.

PATIENTS

There were 1,248 patients.

RESULTS

The GO-based biosensor was oxygen-sensitive. The new GD-based biosensor was oxygen-insensitive. GD-based biosensor performance was acceptable: 2,104 (96.1%) of 2,189 glucose meter measurements were within +/-15 mg/dL (+/-0.83 mmol/L) for glucose levels of < or = 100 mg/dL (< or = 5.55 mmol/L) or within +/-15% for glucose levels of > 100 mg/dL, compared with the whole-blood reference method results. With the GD-based biosensor, the percentages of glucose measurements that were not within the error tolerance were comparable for different specimen types and clinical groups. Bracket predictive values were acceptable for glucose levels used in therapeutic management.

CONCLUSIONS

The performance of GD-based, oxygen-insensitive, handheld glucose testing was technically suitable for arterial specimens in critical care patients, cord blood and heelstick specimens in neonates, and capillary and venous specimens in other patients. Multicenter findings benchmark the performance of bedside glucose testing devices. With the new +/-15 mg/dL --> 100 mg/dL --> +/-15% accuracy criterion, point-of-care systems for handheld glucose testing should score 95% (or better), as compared with the recommended reference method. Physiologic changes, preanalytical factors, confounding variables, and treatment goals must be taken into consideration when interpreting glucose results, especially in critically ill patients, for whom arterial blood glucose measurements will reflect systemic glucose levels.

Ultrasensitive bienzyme sensor for adrenaline

A biosensor consisting of an analyte-recycling two-enzyme system using laccase (Coriolus hirsutus) and PQQ-dependent glucose dehydrogenase in combination with the electrochemical detection of oxygen depletion at a platinum electrode was used for adrenaline determination in the nano- and subnanomolar concentration range. Measurements were performed in a flow cell providing excellent baseline stability and fast recovery of the sensor. Improved design of the polymer matrix resulted in a lower detection limit of 200 pmol/l for adrenaline. The sensor has successfully been applied to the analysis of adrenaline in effluate of isolated rabbit hearts.

Evaluation of HemoCue Blood Glucose Analyzer for the instant diagnosis of hypoglycaemia in newborns

The aim of the study was to evaluate a portable photometer, HemoCue Blood Glucose Analyzer, in the instant diagnosis of hypoglycaemia in newborns. The HemoCue is a simple, easy-to-handle photometer; with an analysis time of less than 240 s, it utilizes a modified glucose dehydrogenase method in 5 microliters whole blood. The HemoCue method was compared to a hexokinase method for deproteinized whole blood in a total of 118 samples from 58 newborns. The linear regression for these samples was Y = 1.19 x -1.02 (range 0.7-7.2 mmol/L), r = 0.90. Ten samples were < or = 2.0 mmol/L with both methods and 37 samples were < or = 2.0 mmol/L with the HemoCue method. The average difference (D) for each sample (n = 118) and the standard deviation (SD) for the difference were 0.45 +/- 0.46 mmol/L. Blood samples with a mean value with both methods < or = 2.0 mmol/L (n = 20) had a D and SD of 0.71 +/- 0.29 mmol/L. When testing for linearity at low glucose concentrations, the HemoCue method gave significantly lower values compared to an ideal line. The HemoCue method has several advantages in the analysis of glucose in newborns: short analysis time, small sample size, and no influence from glycolysis. However, in our investigation, falsely low values occurred, especially in the low measuring range, so the HemoCue method is not suitable in the diagnosis of hypoglycaemia in newborns.

Analysis of tear fluid by CE/LIF: a noninvasive approach for glucose monitoring

Nanoliter volumes of human tear fluid were collected by means of a capillary tube without inducing tearing and were analyzed for glucose content. The tear fluid was subjected to two enzymatic reactions to generate a fluorescent compound that is proportional to the concentration of glucose in the sample. CE with laser-induced fluorescence (LIF) detection was used to monitor the fluorescent species generated, hence glucose in the tear samples. The reproducibility of the method for six different preparations was < 9% relative standard deviation (RSD). The procedure was compared with the glucose dehydrogenase method for the determination of glucose in blood before using it to determine glucose in tear fluid. Blood and tear samples were collected from six healthy human subjects. The results showed that the higher glucose content in tear samples is consistent with the higher glucose content in blood samples. The glucose concentration of the tear samples analyzed ranged from 128 to 166 microM, and that of blood ranged from 3.3 to 4.3 mM.

Poly(methylene blue)-modified thick-film gold electrodes for the electrocatalytic oxidation of NADH and their application in glucose biosensors

Electropolymerization of the phenothiazine derivative methylene blue (MB) on screen-printed, thick-film gold electrodes leads to electrocatalytically active and conducting layers of poly(methylene blue) (PMB) in intimate and stable contact with the electrode surface. The catalytic properties of the PMB films allow anodic oxidation of NADH at potentials as low as +200 mV vs. the saturated calomel electrode (SCE) reducing interferences from cooxidizable species as well as minimizing electrode fouling by enabling a simultaneous two-electron transfer mechanism. Dehydrogenase-based biosensors employing PMB-modified thick-film electrodes are obtained either by entrapment of the enzyme into the PMB layer itself or by laminating an enzyme membrane made of an aqueous poly(vinylacetate) dispersion over the PMB-modified electrode. Both methods are used to fabricate glucose biosensors which can be operated at low overpotentials, i.e. +200 mV vs. SCE.

A new sensitive and simple method for detection of catecholamines from adrenal chromaffin cells

A biosensor was used for the analysis of catecholamines in media and lysates of cultured bovine adrenal chromaffin cells. The sensor is composed of coimmobilised laccase and glucose dehydrogenase coupled with an oxygen electrode, using the catalytic effect of cate cholamines for glucose oxidation in this system. The analysis time is almost 5 min. The correlation between the biosensor and HPLC determination is 0.99.

Amperometric thin film biosensors based on glucose dehydrogenase and Toluidine Blue O as catalyst for NADH electrooxidation

Amperometric glucose sensors were constructed based on solid graphite electrodes, surface-modified with NAD+ dependent glucose dehydrogenase (GDH), Toluidine Blue O (TBO), and protective ionic polymers. The electrocatalytic oxidation of NADH was evaluated from cyclic voltammetry with TBO dissolved, adsorbed, and electrostatically or covalently bound to polymers. The NADH and glucose sensors constructed were investigated and operated at 0 mV vs. Ag/AgCl using single potential step chronoamperometry. The operational stability of the glucose sensors was limited by leakage of NAD+. A glucose sensitivity much higher than carbon paste electrode was found. A sensitivity as high as 25 microA cm-2 mM-1 was achieved.

Biosensor based on an enzyme modified electrode for highly-sensitive measurement of polyphenols

The use of glucose dehydrogenase from Acinetobacter calcoaceticus for highly sensitive measurement of polyphenols, based on bioelectrocatalytic analyte recycling, has been demonstrated. A polyphenol (analyte) is oxidized on the surface of a glassy carbon electrode at an anodic potential and is regenerated by immobilized glucose dehydrogenase (GDH) in the presence of glucose, resulting in an amplified response. The dynamic properties of the enzyme-modified glassy carbon electrode allow the convenient monitoring of subnanomolar analyte concentration. The detection limits for p-aminophenol and norepinephrine are 0.2 nM and 0.5 nM, respectively.

Accuracy of plasma glucose measurements in the hypoglycemic range

OBJECTIVE

This study was designed to evaluate three different enzymatic methods for glucose measurement in plasma samples with special emphasis on glucose concentrations in the hypoglycemic range.

RESEARCH DESIGN AND METHODS

Glucose dehydrogenase (Hemo-Cue analyzer), glucose oxidase (YSI analyzer), and hexokinase (Abbott analyzer) methods were used to measure plasma samples that were obtained during research studies.

RESULTS

Mean glucose concentrations (n = 240) were 5.3 +/- 0.2, 5.4 +/- 0.2, and 5.6 +/- 0.2 mM (95.6 +/- 3.9, 96.7 +/- 3.9, and 101.6 +/- 4.0 mg/dl) using glucose dehydrogenase, glucose oxidase, and hexokinase, respectively (NS). In the hypoglycemic range, mean glucose concentrations with each method retained the same hierarchy of measurements: 2.7 +/- 0.05, 2.8 +/- 0.04, and 2.9 +/- 0.03 mM (48.4 +/- 0.9, 50.6 +/- 0.8, and 52.3 +/- 0.6 mg/dl) by glucose dehydrogenase, glucose oxidase, and hexokinase, respectively (P < 0.005). Individual glucose dehydrogenase measurements (n = 240) correlated well with glucose oxidase and hexokinase, r = 0.99, and were considerably easier to perform at the bedside. The differences between the glucose measurement methods were consistent and similar in low, normal, and high concentration ranges.

CONCLUSIONS

We conclude that any interpretation or comparison of critical clinical and research measurements of glucose in different settings take into account methodological differences, particularly in the hypoglycemic range.

A method for determination of xylose utilizing glucose dehydrogenase

A method is described for xylose determination on the Ciba-Corning 550 Express that utilizes the slower enzymatic action of glucose dehydrogenase (GDH) on D-xylose, after prior removal of glucose. Glucose oxidase is added to serum or urine and incubated for 120 min at 37 degrees C. After incubation, a perchloric acid filtrate of the specimen is added to the GDH reagent in the presence of NAD, the amount of NADH produced being proportional to the amount of xylose present. Absorbances at 340/380 nm are read at 180 s and 600 s after the reagent is added. The standard curve is linear to 7.50 mmol/L and the method showed day-to-day imprecision (CV%) of 2.7 (n = 18), 1.8 (n = 17), and 2.2 (n = 17) at concentrations of 0.62, 1.18, and 2.60 mmol/L, respectively. Recoveries ranged from 99 to 106% for sera and 96 to 100% for urines. Good correlation was obtained when tested against established automated ferricyanide and p-bromoaniline methods.

Flow injection determination of glucose, bile acid and ATP using immobilized enzyme reactor and chemiluminescent assay of NAD(P)H

We have developed a chemiluminescent flow injection method for analysis of bile acid, glucose and ATP using the chemiluminescent assay of NADH using 1-methoxy-5-methylphenazinium methyl sulphate (1-MPMS)/isoluminol(IL)/microperoxidase (m-POD) system and immobilized enzyme reactors such as 3 alpha-hydroxysteroid dehydrogenase, glucose-dehydrogenase, hexokinase and glucose-6-phosphate dehydrogenase. The standard curves were obtained in the range of 5-100 pmol for bile acid, 0.5-5.0 nmol for glucose and 10(-7)-10(-5) mol/L for ATP. The coefficient of variation for each assay was not more than 4.1% for bile acid, 2.3% for glucose and 5.3% for ATP, respectively.

HemoCue: evaluation of a portable photometric system for determining glucose in whole blood

We assessed the HemoCue system for measuring glucose in 5 microL of whole blood. A glucose dehydrogenase-based reaction is used with dried reagents contained in disposable microcuvettes, which are filled with blood by capillary action. Automated hexokinase and YSI 23AM glucose analyzer methods were used for comparison. Overall imprecision (CV) was better than 4.5%, with no significant differences in results between three different HemoCue photometers and four batches of microcuvettes. Regression slopes (+/- SE) were 0.947 (0.011) with the YSI and 0.966 (0.015) with the hexokinase method. Analytical recovery of added glucose was 101-106%, and the system functioned with hematocrits up to 0.65. Bilirubin up to 453 mumol/L did not interfere, but high concentrations of endogenous (greater than 3 mmol/L) and exogenous triglycerides gave positive interference. The system proved stable and robust under a wide range of storage and handling conditions; performance was impaired only at high ambient temperature (37 degrees C). We conclude that the HemoCue system should prove useful for glucose measurement; further testing outside the laboratory is warranted.

Internal supply of coenzyme to an amperometric glucose biosensor based on a chemically modified electrode

A biosensor for glucose using glucose dehydrogenase immobilized on a chemically modified graphite electrode was supplied with coenzyme, nicotinamide adenine dinucleotide (NAD+), through pores in the material. A graphite rod was hollowed out, leaving 0.3 mm at the end contacting the solution, filled with 10 mM NAD+ and pressurized. The response factor was 40% of that obtained when 2 mM NAD+ was mixed with the sample solution in a flow system. The coenzyme consumption was 11 microliters h-1 representing a 500-fold saving compared to supply through the bulk solution. The biosensor had a linear calibration curve from the detection limit, 1 microM, to 2 mM glucose and a repeatability of 0.3%. The graphite electrode was modified by adsorption of a bis-(benzophenoxazinyl)-terephthaloyl derivative in order to be able to oxidize NADH at 0 mV versus Ag/AgCl, 0.1 M KCl.

Problems with the use of whole blood as a sample material in novel direct glucose analysers

We report a marked shift in whole-blood glucose measurements when a widely available glucose analyser is used. We compared a conventional glucose dehydrogenase (GDHG) method after protein precipitation and a direct polarographic method in conjunction with immobilized glucose oxidase. The polarographic method gave mean whole blood glucose levels from 79% to 95% of those measured by the GDHG method. No such difference was found in either plasma or serum samples or in water-based control samples. The stability of glucose in fluoride oxalate tubes appears to be poorer than is usually assumed. We observed a 5-10% decrease in whole-blood glucose concentrations during the first hour after sampling under routine conditions.

Determination of glucose-6-phosphatase activity using the glucose dehydrogenase-coupled reaction

We present a method to determine glucose 6-phosphate activity. This assay measures the rate of glucose released in the glucose-6-phosphatase reaction. The glucose is oxidized to beta-D-gluconolactone by glucose dehydrogenase in a coupled reaction that uses NAD(P)+. The determination is rapid, reproducible, and does not require withdrawal, precipitation, centrifugation, or neutralization steps. This method provides a simple resolution to the problem of the nonspecific appearance of Pi, which is especially important in studies of regulation of glucose-6-phosphatase performed in the presence of ATP.

High-performance liquid chromatographic separation of some mono- and disaccharides with detection by a post-column enzyme reactor and a chemically modified electrode

The effluent from a chromatographic column was mixed with nicotinamide adenine dinucleotide coenzyme (NAD+) buffer and passed through a packed-bed reactor containing immobilized glucose dehydrogenase. Oxidation of the carbohydrates emerging from the column produced an equivalent amount of reduced coenzyme (NADH), which was detected electrochemically using an electrode modified with 7-dimethylamino-1,2-benzophenoxazine (Meldola Blue). Separation was effected in three different chromatographic systems containing a protonated ion exchanger, a calcium(II)-saturated or a lead(II)-saturated ligand exchange column. Separation, detection and k' values are reported for glucose, 2-deoxyglucose, xylose, mannose, cellobiose, lactose, ribose and glucosamine. The detection limit was 2 ng for a 20-microliter injection of glucose and the response was linear up to 6300 ng. Samples from fermentation of penicillin were analysed for lactose and glucose with the described detector. A comparison with the recordings from a refractive index detector showed that the selectivity of the enzymes and the modified electrodes are necessary for the determination of glucose and lactose.

Crystallization of and X-ray investigations on glucose dehydrogenase from Bacillus megaterium

The tetrameric glucose dehydrogenase from Bacillus megaterium M1286 belongs to the 'short' family of dehydrogenases with 262 amino acids per subunit (Mr approximately 30,000), and does not require Zn2+ for enzymatic action. It was crystallized as complex with its coenzyme NAD from a 1-2% protein solution by the batch method using ammonium sulfate as precipitant at pH 6.5. Crystals appeared within two days as clusters of large plates with maximum dimensions of 2 mm, which diffract X-rays to a resolution of at least 0.2 nm. The space group is orthorhombic P2(1)2(1)2(1), unit-cell dimensions are a = 15.03 nm, b = 10.42 nm and c = 6.74 nm. Assuming one molecule (approximately 120 kDa) per asymmetric unit the VM value is 0.0022 nm3/Da and the solvent content of the crystals is 45% based on a partial specific volume for the protein of 0.723 ml/g. The crystallization was further improved by using the microdialysis technique where instead of clusters, single crystals appeared within 7 days.

Enzymatic determination of pyrroloquinoline quinone using crude membranes from Escherichia coli

Escherichia coli K-12 (ATCC 10 798) contains only the apoform of membrane-bound D-glucose dehydrogenase (pyrroloquinoline quinone-dependent). Crude membrane preparations or even crude cell extracts are suitable for a sensitive determination of pyrroloquinoline quinone under appropriate conditions. The apoform of D-glucose dehydrogenase from E. coli is reconstituted with pyrroloquinoline quinone to the holoenzyme in the presence of Mg2+ and assayed for glucose dehydrogenase activity. By increasing the time of reconstitution it is possible to detect minute amounts of about 20 pg pyrroloquinoline quinone.