Pyrroloquinoline quinone-dependent carbohydrate dehydrogenase: Activity enhancement and the role of artificial electron acceptors

Pourbiax Diagrams as an Aid to Understanding the Impact of Acid/Base Disturbance on Blood Glucose Point-of-Care Testing

OBJECTIVE

Assays based on redox reactions that involve proton transfer are vulnerable to artifactual findings in metabolic acidosis/alkalosis. We evaluated the impact of pH on the measurement of blood glucose by the glucose dehydrogenase/pyrroloquinoline quinone system used in point-of-care-testing.

METHODS

We applied a series of thermodynamic equations to adjust the Gibbs energy for the pyrroloquinoline quinone couple. This adjusts values taken under standard conditions to those more closely resembling the physiological state.

RESULTS

Under standard conditions, the pyrroloquinoline quinone couple has Eo = -0.125 V whereas adjustment to the physiological state (pH 7.40, ionic strength 0.15 mol/L, and temperature 310.15°K) yields Eo' = -0.166 V. This corresponds to an uncertainty in blood glucose determination of approximately 0.13 mmol/L.

CONCLUSION

We have demonstrated that the impact of pH on blood glucose determination by the glucose dehydrogenase/pyrroloquinoline quinone system (under physiologically relevant conditions of ionic strength and temperature) is not clinically significant.

PQQ-GDH - Structure, function and application in bioelectrochemistry

This review summarizes the basic features of the PQQ-GDH enzyme as one of the sugar converting biocatalysts. Focus is on the membrane -bound and the soluble form. Furthermore, the main principles of enzymatic catalysis as well as studies on the physiological importance are reviewed. A short overview is given on developments in protein engineering. The major part, however, deals with the different fields of application in bioelectrochemistry. This includes approaches for enzyme-electrode communication such as direct electron transfer, mediator-based systems, redox polymers or conducting polymers and holoenzyme reconstitution, and covers applied areas such as biosensing, biofuel cells, recycling schemes, enzyme competition, light-directed sensing, switchable detection schemes, logical operations by enzyme electrodes and immune sensing.

Critical Care Glucose Point-of-Care Testing

Maintaining blood glucose concentration within an acceptable range is a goal for patients with diabetes mellitus. Point-of-care glucose meters initially designed for home self-monitoring in patients with diabetes have been widely used in the hospital settings because of ease of use and quick reporting of blood glucose information. They are not only utilized for the general inpatient population but also for critically ill patients. Many factors affect the accuracy of point-of-care glucose testing, particularly in critical care settings. Inaccurate blood glucose information can result in unsafe insulin delivery which causes poor glucose control and can be fatal. Healthcare professionals should be aware of the limitations of point-of-care glucose testing. This chapter will first introduce glucose regulation in diabetes mellitus, hyperglycemia/hypoglycemia in the intensive care unit, importance of glucose control in critical care patients, and pathophysiological variables of critically ill patients that affect the accuracy of point-of-care glucose testing. Then, we will discuss currently available point-of-care glucose meters and preanalytical, analytical, and postanalytical sources of variation and error in point-of-care glucose testing.

Computational modeling of mediator oxidation by oxygen in an amperometric glucose biosensor

In this paper, an amperometric glucose biosensor is modeled numerically. The model is based on non-stationary reaction-diffusion type equations. The model consists of four layers. An enzyme layer lies directly on a working electrode surface. The enzyme layer is attached to an electrode by a polyvinyl alcohol (PVA) coated terylene membrane. This membrane is modeled as a PVA layer and a terylene layer, which have different diffusivities. The fourth layer of the model is the diffusion layer, which is modeled using the Nernst approach. The system of partial differential equations is solved numerically using the finite difference technique. The operation of the biosensor was analyzed computationally with special emphasis on the biosensor response sensitivity to oxygen when the experiment was carried out in aerobic conditions. Particularly, numerical experiments show that the overall biosensor response sensitivity to oxygen is insignificant. The simulation results qualitatively explain and confirm the experimentally observed biosensor behavior.

Blood‐Glucose Biosensors, Development and Challenges

Diabetes mellitus is one of the major causes of premature illness and death worldwide. The World Health Organization estimated that by 2030, 439 million people, corresponding to 7.8% of the world adult population, will live with diabetes. With an increasing diabetic population, a Blood Glucose Monitoring System (BGMS) is becoming an ever important tool for diabetes management. The history of blood biosensor development can be traced back to 1932, when Warburg and Christian reported the “yellow enzyme” from yeast changed to colorless upon oxidizing its substrate and resumed the yellow color after its oxidation by oxygen. Since then a lot of research and development has taken place on blood glucose sensors, and the biosensor technology has gone through three generations, with the current commercially available BGMS predominantly relies on the second generation of technology. The advantages and challenges of each generation are discussed. This chapter will examine in detail topics covering the areas of electrode substrate and electrode material selection, fluid detection electrode, reaction chamber, chemistry (electrolyte, polymer, enzyme and mediator), detection method, analytical performance, regulatory requirements and the manufacturing process. The chapter will close with the clinical utility and future direction and application of glucose biosensor include a brief introduction to the Continuous Blood Glucose Monitoring System (CGMS).

Modelling of amperometric biosensor used for synergistic substrates determination

In this paper the operation of an amperometric biosensor producing a chemically amplified signal is modelled numerically. The chemical amplification is achieved by using synergistic substrates. The model is based on non-stationary reaction-diffusion equations. The model involves three layers (compartments): a layer of enzyme solution entrapped on the electrode surface, a dialysis membrane covering the enzyme layer and an outer diffusion layer which is modelled by the Nernst approach. The equation system is solved numerically by using the finite difference technique. The biosensor response and sensitivity are investigated by altering the model parameters influencing the enzyme kinetics as well as the mass transport by diffusion. The biosensor action was analyzed with a special emphasis to the effect of the chemical amplification. The simulation results qualitatively explain and confirm the experimentally observed effect of the synergistic substrates conversion on the biosensor response.

High-throughput screening for cellobiose dehydrogenases by Prussian Blue in situ formation

Extracellular fungal flavocytochrome cellobiose dehydrogenase (CDH) is a promising enzyme for both bioelectronics and lignocellulose bioconversion. A selective high-throughput screening assay for CDH in the presence of various fungal oxidoreductases was developed. It is based on Prussian Blue (PB) in situ formation in the presence of cellobiose (<0.25 mM), ferric acetate, and ferricyanide. CDH induces PB formation via both reduction of ferricyanide to ferrocyanide reacting with an excess of Fe³⁺ (pathway 1) and reduction of ferric ions to Fe²⁺ reacting with the excess of ferricyanide (pathway 2). Basidiomycetous and ascomycetous CDH formed PB optimally at pH 3.5 and 4.5, respectively. In contrast to the holoenzyme CDH, its FAD-containing dehydrogenase domain lacking the cytochrome domain formed PB only via pathway 1 and was less active than the parent enzyme. The assay can be applied on active growing cultures on agar plates or on fungal culture supernatants in 96-well plates under aerobic conditions. Neither other carbohydrate oxidoreductases (pyranose dehydrogenase, FAD-dependent glucose dehydrogenase, glucose oxidase) nor laccase interfered with CDH activity in this assay. Applicability of the developed assay for the selection of new ascomycetous CDH producers as well as possibility of the controlled synthesis of new PB nanocomposites by CDH are discussed.