Thermal inactivation of glucose oxidase. Mechanism and stabilization using additives

Non-enzymatic electrochemical glucose sensor based on NiMoO₄ nanorods

A non-enzymatic glucose sensor based on the NiMoO4 nanorods has been fabricated for the first time. The electrocatalytic performance of the NiMoO4 nanorods' modified electrode toward glucose oxidation was evaluated by cyclic voltammetry and amperometry. The NiMoO4 nanorods' modified electrode showed a greatly enhanced electrocatalytic property toward glucose oxidation, as well as an excellent anti-interference and a good stability. Impressively, good accuracy and high precision for detecting glucose concentration in human serum samples were obtained. These excellent sensing properties, combined with good reproducibility and low cost, indicate that NiMoO4 nanorods are a promising candidate for non-enzymatic glucose sensors.

Enhanced thermal stability and pH behavior of glucose oxidase on electrostatic interaction with polyethylenimine

Electrostatic interactions, mediated by ionic-exchange, between polyethylenimine (PEI) and glucose oxidase (GOx) were used to form GOx-PEI macro-complex, which were evaluated for pH and thermal stability of GOx. Under the experimental conditions, the complex had a dominant GOx presence on its surface and a hydrodynamic diameter of 205 ± 16 nm. Activity was evaluated from 40 to 75 °C, and at pH from 2 to 12. GOx activity in complex was maintained up to 70 °C and it was lost at 75 °C. In contrast, free GOx showed a maximum activity at 50 °C, which was completely lost at 70 °C. This difference, observed by fluorescence analysis, was associated with the compact unfolded structure of GOx in the complex. This GOx stability was not observed under pH variations, and complex formation was only possible at pH ≥ 5 where enzymatic activity was diminished by the presence of PEI.

Electrochemical Glucose Biosensor Based on Glucose Oxidase Displayed on Yeast Surface

The conventional enzyme-based biosensor requires chemical or physical immobilization of purified enzymes on electrode surface, which often results in loss of enzyme activity and/or fractions immobilized over time. It is also costly. A major advantage of yeast surface display is that it enables the direct utilization of whole cell catalysts with eukaryote-produced proteins being displayed on the cell surface, providing an economic alternative to traditional production of purified enzymes. Herein, we describe the details of the display of glucose oxidase (GOx) on yeast cell surface and its application in the development of electrochemical glucose sensor. In order to achieve a direct electrochemistry of GOx, the entire cell catalyst (yeast-GOx) was immobilized together with multiwalled carbon nanotubes on the electrode, which allowed sensitive and selective glucose detection.

Vulnerability of point-of-care test reagents and instruments to environmental stresses: implications for health professionals and developers

Strategic integration of point-of-care (POC) diagnostic tools during crisis response can accelerate triage and improve management of victims. Timely differential diagnosis is essential wherever care is provided to rule out or rule in disease, expedite life-saving treatment, and improve utilization of limited resources. POC testing needs to be accurate in any environment in which it is used. Devices are exposed to potentially adverse storage and operating conditions, such as high/low temperature and humidity during emergencies and field rescues. Therefore, characterizing environmental conditions allows technology developers, operators, and responders to understand the broad operational requirements of test reagents, instruments, and equipment in order to improve the quality and delivery of care in complex emergencies, disasters, and austere environmental settings. This review aims to describe the effects of environmental stress on POC testing performance and its impact on decision-making, to describe how to study the effects, and to summarize ways to mitigate the effects of environmental stresses through good laboratory practice, development of robust reagents, and novel thermal packaging solutions.

New insights into heat induced structural changes of pectin methylesterase on fluorescence spectroscopy and molecular modeling basis

Heat-induced structural changes of Aspergillus oryzae pectin methylesterase (PME) were studied by means of fluorescence spectroscopy and molecular modeling, whereas the functional enzyme stability was monitored by inactivation studies. The fluorescence spectroscopy experiments were performed at two pH value (4.5 and 7.0). At both pH values, the phase diagrams were linear, indicating the presence of two molecular species induced by thermal treatment. A red shift of 7 nm was observed at neutral pH by increasing temperature up to 60°C, followed by a blue shift of 4 nm at 70°C, suggesting significant conformational rearrangements. The quenching experiments using acrylamide and iodide demonstrate a more flexible conformation of enzyme with increasing temperature, especially at neutral pH. The experimental results were complemented with atomic level observations on PME model behavior after performing molecular dynamics simulations at different temperatures. The inactivation kinetics of PME in buffer solutions was fitted using a first-order kinetics model, resulting in activation energy of 241.4±7.51 kJ mol(-1).

Enzyme immobilization on silane-modified surface through short linkers: fate of interfacial phases and impact on catalytic activity

We investigated the mechanism of enzyme immobilization on silanized surfaces through coupling agents (cross-linkers) in order to understand the role of these molecules on interfacial processes and their effect on catalytic activity. To this end, we used a model multimeric enzyme (G6PDH) and several cross-linking molecules with different chemical properties, including the nature of the end-group (-NCO, -NCS, -CHO), the connecting chain (aliphatic vs aromatic), and geometrical constraints (meta vs para-disubstituted aromatics). There did not seem to be radical differences in the mechanism of enzyme adsorption according to the linker used as judged from QCM-D, except that in the case of DIC (1,4-phenylene diisocyanate) the adsorption occurred more rapidly. In contrast, the nature of the cross-linker exerted a strong influence on the amount of enzyme immobilized as estimated from XPS, and more unexpectedly on the stability of the underlying silane layer. DIC, PDC (1,4-phenylene diisothiocyanate), or GA (glutaraldehyde) allowed successful enzyme immobilization. When the geometry of the linker was changed from 1,4-phenylene diisothiocyanate to 1,3-phenylene diisothiocyanate (MDC), the silane layer was subjected to degradation, upon enzyme adsorption, and the amount of immobilized molecules was significantly lowered. TE (terephtalaldehyde) and direct enzyme deposition without cross-linker were similar to MDC. The organization of immobilized enzymes also depended on the immobilization procedure, as different degrees of aggregation were observed by AFM. A correlation between the size of the aggregates and the catalytic properties of the enzyme was established, suggesting that aggregation may enhance the thermostability of the multimeric enzyme, probably through a compaction of the 3D structure.

Enhancing enzyme stability by construction of polymer-enzyme conjugate micelles for decontamination of organophosphate agents

Enhancing the stability of enzymes under different working environments is essential if the potential of enzyme-based applications is to be realized for nanomedicine, sensing and molecular diagnostics, and chemical and biological decontamination. In this study, we focus on the enzyme, organophosphorus hydrolase (OPH), which has shown great promise for the nontoxic and noncorrosive decontamination of organophosphate agents (OPs) as well as for therapeutics as a catalytic bioscavanger against nerve gas poisoning. We describe a facile approach to stabilize OPH using covalent conjugation with the amphiphilic block copolymer, Pluronic F127, leading to the formation of F127-OPH conjugate micelles, with the OPH on the micelle corona. SDS-PAGE and MALDI-TOF confirmed the successful conjugation, and transmission electron microscopy (TEM) and dynamic light scattering (DLS) revealed ∼100 nm size micelles. The conjugates showed significantly enhanced stability and higher activity compared to the unconjugated OPH when tested (i) in aqueous solutions at room temperature, (ii) in aqueous solutions at higher temperatures, (iii) after multiple freeze/thaw treatments, (iv) after lyophilization, and (v) in the presence of organic solvents. The F127-OPH conjugates also decontaminated paraoxon (introduced as a chemical agent simulant) on a polystyrene film surface and on a CARC (Chemical Agent Resistant Coating) test panel more rapidly and to a larger extent compared to free OPH. We speculate that, in the F127-OPH conjugates (both in the micellar form as well as in the unaggregated conjugate), the polypropylene oxide block of the copolymer interacts with the surface of the OPH and this confinement of the OPH reduces the potential for enzyme denaturation and provides robustness to OPH at different working environments. The use of such polymer-enzyme conjugate micelles with improved enzyme stability opens up new opportunities for numerous civilian and Warfighter applications.

Enzymes as bionanoreactors: glucose oxidase for the synthesis of catalytic Au nanoparticles and Au nanoparticle–polyaniline nanocomposites

Biogenic synthesis of Au nanoparticles and Au nanoparticle–polyaniline composite could be accomplished taking advantage of the reducing and catalytic activity of glucose oxidase.

Short-Term Thermal-Humidity Shock Affects Point-of-Care Glucose Testing: Implications for Health Professionals and Patients

The objective was to assess the effects of short-term (≤1 hour) static high temperature and humidity stresses on the performance of point-of-care (POC) glucose test strips and meters. Glucose meters are used by medical responders and patients in a variety of settings including hospitals, clinics, homes, and the field. Reagent test strips and instruments are potentially exposed to austere environmental conditions. Glucose test strips and meters were exposed to a mean relative humidity of 83.0% (SD = 8.0%) and temperature of 42°C (107.6°F, SD = 3.2) in a Tenney BTRC environmental chamber. Stressed and unstressed glucose reagent strips and meters were tested with spiked blood samples (n = 40 measurements per time point for each of 4 trials) after 15, 30, 45, and 60 minutes of exposure. Wilcoxon's signed rank test was applied to compare measurements test strip and meter measurements to isolate and characterize the magnitude of meter versus test strip effects individually. Stressed POC meters and test strips produced elevated glucose results, with stressed meter bias as high as 20 mg/dL (17.7% error), and stressed test strip bias as high as 13 mg/dL (12.2% error). The aggregate stress effect on meter and test strips yielded a positive bias as high as 33 mg/dL (30.1% error) after 15 minutes of exposure. Short-term exposure (15 minutes) to high temperature and humidity can significantly affect the performance of POC glucose test strips and meters, with measurement biases that potentially affect clinical decision making and patient safety.

Synthesis of graphene oxide based CuO nanoparticles composite electrode for highly enhanced nonenzymatic glucose detection

CuO nanoparticles (NPs) based graphene oxide (CuO/GO) composites with different CuO NPs loading amount as well as pure CuO NPs with different hydrothermal temperatures were synthesized using a hydrothermal method. Transmission electron microscopy (TEM), X-ray diffraction (XRD), thermogravimetric analysis (TGA), and Raman spectroscopy were employed to characterize the morphology and structures of our samples. The influence of hydrothermal temperature, GO sheet, and loading amount of CuO on particle size and structure of CuO was systemically investigated. The nonenzymatic biosensing properties of CuO/GO composites and CuO NPs toward glucose were studied based on glassy carbon electrode (GCE). The sensing properties of CuO NPs were improved after loading on GO sheets. The CuO/GO composites with saturated loading of the CuO NPs exhibited the best nonenzymatic biosensing behavior. It exhibited a sensitivity of 262.52 μA mM(-1) cm(-2) to glucose with a 0.69 μM detection limit (S/N = 3) and a linear range from 2.79 μM to 2.03 mM under a working potential of +0.7 V. It also showed outstanding long term stability, good reproducibility, excellent selectivity, and accurate measurement in real serum sample. It is believed that CuO/GO composites show good promise for further application on nonenzymatic glucose biosensors.

Characterization of AmiBA2446, a novel bacteriolytic enzyme active against Bacillus species

There continues to be a need for developing efficient and environmentally friendly treatments for Bacillus anthracis, the causative agent of anthrax. One emerging approach for inactivation of vegetative B. anthracis is the use of bacteriophage endolysins or lytic enzymes encoded by bacterial genomes (autolysins) with highly evolved specificity toward bacterium-specific peptidoglycan cell walls. In this work, we performed in silico analysis of the genome of Bacillus anthracis strain Ames, using a consensus binding domain amino acid sequence as a probe, and identified a novel lytic enzyme that we termed AmiBA2446. This enzyme exists as a homodimer, as determined by size exclusion studies. It possesses N-acetylmuramoyl-l-alanine amidase activity, as determined from liquid chromatography-mass spectrometry (LC-MS) analysis of muropeptides released due to the enzymatic digestion of peptidoglycan. Phylogenetic analysis suggested that AmiBA2446 was an autolysin of bacterial origin. We characterized the effects of enzyme concentration and phase of bacterial growth on bactericidal activity and observed close to a 5-log reduction in the viability of cells of Bacillus cereus 4342, a surrogate for B. anthracis. We further tested the bactericidal activity of AmiBA2446 against various Bacillus species and demonstrated significant activity against B. anthracis and B. cereus strains. We also demonstrated activity against B. anthracis spores after pretreatment with germinants. AmiBA2446 enzyme was also stable in solution, retaining its activity after 4 months of storage at room temperature.

Heated proteins are still active in a functionalized nanoporous support

Even under heated conditions, the nearly native conformation and activity of a protein can be hoarded in a functionalized nanoporous support via non-covalent interaction. Surprisingly, the protein released from the heated protein-nanoporous composite can maintain its nearly native conformation and activity, while free proteins are permanently denatured under the same treatment.

Effects of dynamic temperature and humidity stresses on point-of-care glucose testing for disaster care

OBJECTIVE

To characterize the performance of glucose meter test strips using simulated dynamic temperature and humidity disaster conditions.

METHODS

Glucose oxidase- and glucose dehydrogenase-based test strips were dynamically stressed for up to 680 hours using an environmental chamber to simulate conditions during Hurricane Katrina. Paired measurements vs control were obtained using 3 aqueous reagent levels for GMS1 and 2 for GMS2.

RESULTS

Stress affected the performance of GMS1 at level 1 (P < .01); and GMS2 at both levels (P < .001), lowering GMS1 results but elevating GMS2 results. Glucose median-paired differences were elevated at both levels on GMS2 after 72 hours. Median-paired differences (stress minus control) were as much as -10 mg/dL (range, -65 to 33) at level 3 with GMS1, with errors as large as 21.9%. Glucose median-paired differences were as high as 5 mg/dL (range, -1 to 10) for level 1 on GMS2, with absolute errors up to 24.4%.

CONCLUSIONS

The duration of dynamic stress affected the performance of both GMS1 and GMS2 glucose test strips. Therefore, proper monitoring, handling, and storage of point-of-care (POC) reagents are needed to ensure their integrity and quality of actionable results, thereby minimizing treatment errors in emergency and disaster settings.

Glycosylation site-targeted PEGylation of glucose oxidase retains native enzymatic activity

Targeted PEGylation of glucose oxidase at its glycosylation sites was investigated to determine the effect on enzymatic activity, as well as the bioconjugate's potential in an optical biosensing assay. Methoxy-poly(ethylene glycol)-hydrazide (4.5kDa) was covalently coupled to periodate-oxidized glycosylation sites of glucose oxidase from Aspergillus niger. The bioconjugate was characterized using gel electrophoresis, liquid chromatography, mass spectrometry, and dynamic light scattering. Gel electrophoresis data showed that the PEGylation protocol resulted in a drastic increase (ca. 100kDa) in the apparent molecular mass of the protein subunit, with complete conversion to the bioconjugate; liquid chromatography data corroborated this large increase in molecular size. Mass spectrometry data proved that the extent of PEGylation was six poly(ethylene glycol) chains per glucose oxidase dimer. Dynamic light scattering data indicated the absence of higher-order oligomers in the PEGylated GOx sample. To assess stability, enzymatic activity assays were performed in triplicate at multiple time points over the course of 29 days in the absence of glucose, as well as before and after exposure to 5% w/v glucose for 24h. At a confidence level of 95%, the bioconjugate's performance was statistically equivalent to native glucose oxidase in terms of activity retention over the 29 day time period, as well as following the 24h glucose exposure. Finally, the bioconjugate was entrapped within a poly(2-hydroxyethyl methacrylate) hydrogel containing an oxygen-sensitive phosphor, and the construct was shown to respond approximately linearly with a 220±73% signal change (n=4, 95% confidence interval) over the physiologically-relevant glucose range (i.e., 0-400mg/dL); to our knowledge, this represents the first demonstration of PEGylated glucose oxidase incorporated into an optical biosensing assay.

Silk materials--a road to sustainable high technology

This review addresses the use of silk protein as a sustainable material in optics and photonics, electronics and optoelectronic applications. These options represent additional developments for this technology platform that compound the broad utility and impact of this material for medical needs that have been recently described in the literature. The favorable properties of the material certainly make a favorable case for the use of silk, yet serve as a broad inspiration to further develop biological foundries for both the synthesis and processing of Nature's materials for technological applications.

Engineering the interface between glucose oxidase and nanoparticles

The behavior of glucose oxidase (GOx) on gold nanoparticles (NPs) was investigated as a function of (1) NP surface chemistry, (2) stabilizing protein additives, and (3) protein microenvironment. GOx secondary structure and unfolding was probed by circular dichroism (CD) spectroscopy and fluorescence, and GOx enzymatic activity was measured by a colorimetric assay. We also examined the activity and structure of GOx after displacement from the NP surface. Generally, GOx behavior was negatively impacted by conjugation to the NP, and conjugation conditions could vary the influence of the NP. Surface chemistry and protein microenvironment could improve behavior, but addition of stabilizing proteins negatively influenced activity. After displacement from the NPs, GOx tended to remain unfolded, indicating that the interactions with the NP were irreversible.

In vitro influence of D/L-lactic acid, sodium chloride and sodium nitrite on the infectivity of feline calicivirus and of ECHO virus as potential surrogates for foodborne viruses

The importance of foodborne viruses is increasingly recognized. Thus, the effect of commonly used food preservation methods on the infectivity of viruses is questioned. In this context, we investigated the antiviral properties of D,L-lactic acid, sodium chloride and sodium nitrite by in vitro studies. Two model viruses, Feline Calicivirus (FCV) and Enteric Cytophatic Human Orphan (ECHO) virus, were chosen for this study simulating important foodborne viruses (human noroviruses (NoV) and human enteroviruses, resp.). The model viruses were exposed to different solutions of D,L-lactic acid (0.1-0.4% w/w, pH 6.0-3.2), of sodium chloride (2-20%, w/v) and of sodium nitrite (100, 150 and 200 ppm) at 4 and 20 °C for a maximum of 7 days. Different results were obtained for the two viruses. ECHO virus was highly stable against D,L-lactic acid and sodium chloride when tested under all conditions. On the contrary, FCV showed less stability but was not effectively inactivated when exposed to low acid and high salt conditions at refrigeration temperatures (4 °C). FCV titers decreased more markedly at 20 °C than 4 °C in all experiments. Sodium nitrite did not show any effect on the inactivation of both viruses. The results indicate that acidification, salting or curing maybe insufficient for effective inactivation of foodborne viruses such as NoV or human enteroviruses during food processing. Thus, application of higher temperature during fermentation and ripening processes maybe more effective toward the inactivation kinetics of less stable viruses. Nevertheless, more studies are needed to examine the antiviral properties of these preserving agents on virus survival and inactivation kinetics in the complex food matrix.

Additive effect of dextrans on the stability of horseradish peroxidase

The influence of various concentration (10, 20, and 30% w/v) of different molar weighted dextrans as additives on the stability of HRP has been studied in aqueous medium. Native HRP preparations were formulated with different additives for storage stabilization and better performance at high temperature and pH. The results obtained show a stabilizing effect in the presence of an additive (75 kDa dextran). The enzyme with 75 kDa dextran (in concentration 10% w/v) showed the highest thermal resistance and the best performance for long-term storage at pH 5.0. In the presence of the 75 kDa dextran, the enzyme activity was increased threefold at 25 °C and lost only 15% activity in 2 h at 50 °C in comparison to the native enzyme which lost all its activity. In addition, dextran protected HRP against inactivation by air bubbles.

The mechanism of inactivation of glucose oxidase from Penicillium amagasakiense under ambient storage conditions

Glucose oxidase (GOx) from Penicillium amagasakiense has a higher specific activity than the more commonly studied Aspergillus niger enzyme, and may therefore be preferred in many medical and industrial applications. The enzyme rapidly inactivates on storage at pH 7.0-7.6 at temperatures between 30 and 40°C. Results of fluorimetry and circular dichroism spectroscopy indicate that GOx inactivation under these conditions is associated with release of the cofactor FAD and molten globule formation, indicated by major loss of tertiary structure but almost complete retention of secondary structure. Inactivation of GOx at pH<7 leads to precipitation, but at pH ≥ 7 it leads to non-specific formation of small soluble aggregates detectable by PAGE and size-exclusion chromatography (SEC). Inactivation of P. amagasakiense GOx differs from that of A. niger GOx in displaying complete rather than partial retention of secondary structure and in being promoted rather than prevented by NaCl. The contrasting salt effects may reflect differences in the nature of the interface between subunits in the native dimers and/or the quantity of secondary structure loss upon inactivation.

Organic-soluble enzyme nano-complexes formed by ion-pairing with surfactants

The solubilization of enzymes in organic solvents for non-aqueous biocatalysis has attracted considerable attention since the homogeneous distribution accounts for a drastically improved reaction efficiency compared to enzymes dispersed as aggregates in an organic phase. This chapter highlights ion-pairing as a valuable and facile method to make enzymes soluble in organic solvents. Ion-pairing denotes the formation of a nano-complex, in which a single enzyme molecule in the core is surrounded by counter-charged surfactant molecules. The special architecture of this nano-complex exposes the surfactant hydrophobic group toward the bulk solvent and renders the complex sufficiently soluble in organic media. This chapter also describes the underlying principle of ion-pairing as well as simple preparation and characterization techniques to yield highly active enzyme-surfactant nano-complexes. The general applicability of this technique is demonstrated on the base of the hydrolytic enzyme α-chymotrypsin (α-CT) and the redox enzyme glucose oxidase (GO( x )).

Influence of pH and sodium chloride on kinetics of thermal inactivation of the bacteriocin-like substance P34

AIMS

To investigate the kinetics of thermal inactivation of the bacteriocin-like substance P34 at different pH and sodium chloride concentration.

METHODS AND RESULTS

Samples of bacteriocin were treated at different time-temperature combinations in the range of 0-300 min and 90-120°C and the kinetic parameters for bacteriocin inactivation were calculated. For all treatments, the thermal inactivation reaction fitted adequately to first-order model. D- and k-values were smaller and higher, respectively, for pH 4·5 than for 6·0 or 7·0, indicating that bacteriocin P34 was less thermostable at lower pH. At 120, 115 and 100°C, the addition of sodium chloride decreased thermal stability. For other temperatures, addition of NaCl increased stability of the peptide. The presence of greater amount of the salt (50 g l(-1) ) resulted in a higher thermal stability of bacteriocin P34, suggesting that the reduction in water activity of the solution interfered on the stability of the peptide.

CONCLUSIONS

Based on an isothermal experiment in the temperature range of 90-120°C, and by thermal death time models, bacteriocin P34 is less heat stable at low pH and has increased thermal stability in the presence of NaCl. Addition of NaCl improved the stability of the peptide P34 at high temperatures.

SIGNIFICANCE AND IMPACT OF THE STUDY

Studies on kinetics of thermal inactivation of bacteriocins are essential to allow their proper utilization in the food industry.

Amyloid fibrils as a nanoscaffold for enzyme immobilization

Amyloid fibrils are a misfolded state, formed by many proteins when subjected to denaturing conditions. Their constituent amino acids make them ideally suited as a readily functionalized nanoscaffold for enzyme immobilization and their strength, stability, and nanometer size are attractive features for exploitation in the creation of new bionanomaterials. We report successful functionalization of amyloid fibrils by conjugation to glucose oxidase (GOD) using glutaraldehyde. GOD retained activity upon attachment and successful cross-linking was determined using electrophoresis, centrifugation, sucrose gradient centrifugation, and TEM. The resulting functionalized enzyme scaffold was then incorporated into a model poly(vinyl alcohol) (PVOH) film, to create a new bionanomaterial. The antibacterial effect of the functionalized film was then tested on E. coli, the growth of which was inhibited, demonstrating the incorporation of GOD antibacterial activity into the PVOH film. The incorporation of the GOD-functionalized amyloid fibrils into PVOH provides an excellent 'proof of concept' model for the creation of a new bionanomaterial using a functionalized amyloid fibril scaffold.

Heterologous expression of glucose oxidase in the yeast Kluyveromyces marxianus

BACKGROUND

In spite of its advantageous physiological properties for bioprocess applications, the use of the yeast Kluyveromyces marxianus as a host for heterologous protein production has been very limited, in constrast to its close relative Kluyveromyces lactis. In the present work, the model protein glucose oxidase (GOX) from Aspergillus niger was cloned into K. marxianus CBS 6556 and into K. lactis CBS 2359 using three different expression systems. We aimed at verifying how each expression system would affect protein expression, secretion/localization, post-translational modification, and biochemical properties.

RESULTS

The highest GOX expression levels (1552 units of secreted protein per gram dry cell weight) were achieved using an episomal system, in which the INU1 promoter and terminator were used to drive heterologous gene expression, together with the INU1 prepro sequence, which was employed to drive secretion of the enzyme. In all cases, GOX was mainly secreted, remaining either in the periplasmic space or in the culture supernatant. Whereas the use of genetic elements from Saccharomyces cerevisiae to drive heterologous protein expression led to higher expression levels in K. lactis than in K. marxianus, the use of INU1 genetic elements clearly led to the opposite result. The biochemical characterization of GOX confirmed the correct expression of the protein and showed that K. marxianus has a tendency to hyperglycosylate the protein, in a similar way as already observed for other yeasts, although this tendency seems to be smaller than the one of e.g. K. lactis and S. cerevisiae. Hyperglycosylation of GOX does not seem to affect its affinity for the substrate, nor its activity.

CONCLUSIONS

Taken together, our results indicate that K. marxianus is indeed a good host for the expression of heterologous proteins, not only for its physiological properties, but also because it correctly secretes and folds these proteins.

Stabilization of enzymes in silk films

Material systems are needed that promote stabilization of entrained molecules, such as enzymes or therapeutic proteins, without destroying their activity. We demonstrate that the unique structure of silk fibroin protein, when assembled into the solid state, establishes an environment that is conducive to the stabilization of entrained proteins. Enzymes (glucose oxidase, lipase, and horseradish peroxidase) entrapped in these films over 10 months retained significant activity, even when stored at 37 degrees C, and in the case of glucose oxidase did not lose any activity. Further, the mode of processing of the silk protein into the films could be correlated to the stability of the enzymes. The relationship between processing and stability offers a large suite of conditions within which to optimize such stabilization processes. Overall, the techniques reported here result in materials that stabilize enzymes to an extent, without the need for cryoprotectants, emulsifiers, covalent immobilization, or other treatments. Further, these systems are amenable to optical applications and characterization, environmental distribution without refrigeration, are ingestible, and offer potential use in vivo, because silk materials are biocompatible and FDA approved, degradable with proteases, and currently used in biomedical devices.

Thermal stress and point-of-care testing performance: suitability of glucose test strips and blood gas cartridges for disaster response

OBJECTIVE

Point-of-care testing (POCT) devices are deployed in the field for emergency on-site testing under a wide range of environmental conditions. Our objective was to evaluate the performance of glucose meter test strips and handheld blood gas analyzer cartridges following thermal stresses that simulate field conditions.

METHODS

We evaluated electrochemical and spectrophotometric glucose meter systems and a handheld blood gas analyzer. Glucose test strips were cold-stressed (-21 degrees C) and heat-stressed (40 degrees C) for up to 4 weeks. Blood gas cartridges were stressed at -21 degrees C, 2 degrees C, and 40 degrees C for up to 72 hours. Test strip and cartridge performance was evaluated using aqueous quality control solutions. Results were compared with those obtained with unstressed POCT strips and cartridges.

RESULTS

Heated glucose test strips and blood gas cartridges yielded elevated results. Frozen test strips and cooled cartridges yielded depressed glucose and blood gas results, respectively. Frozen cartridges failed.

CONCLUSIONS

The performance of glucose test strips and blood gas cartridges was affected adversely by thermal stresses. Heating generated elevated results, and cooling depressed results. Disaster medical assistance teams and emergency medical responders should be aware of these risks. Field POCT devices must be robust to withstand adverse conditions. We recommend that industry produce POCT devices and reagents suitable for disaster medical assistance teams.