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Glucose oxidase has had a central role in previous glucose sensing methods and is key to the development of certain new glucose sensors. The immobilized enzyme is specific for glucose and sufficiently long-lived for many sensor applications, but new glucose sensing applications may place increased demands on the enzyme.
Strains of microorganisms (13) producing enzyme glucoseoxidase were isolated from various samples of soil. The ability to oxidase glucose in presence of oxygen is most expressed in representatives of genera Aureobasidium, Aspergillus, Penicillium. Media containing the KJ-starch indicator were used at primary step for isolation of microorganisms from the environment. The strain, identified as Aureobasidium pullulans (de Bary) Arnaud, isolated from soil had the greatest glucoseoxidase activity, remained active after lyophilization, grew on the medium, which contained low concentration of glucose and nitrate for candides. Use of its cells as a glucoseoxidase sensor control allowed to detect glucose in the liquids with concentration from 0.027 mM/l.
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The most widely used method for estimation of plasma glucose is that adopted by Trinder's using glucose oxidase-peroxidase (GOD-POD) system. This method gives much lower blood glucose values with blood samples of neonatal jaundice (plasma bilirubin level > 10 mg/dL) of age 10 +/- 5 daysthan with samples of neonates of the same age group without jaundice or older children suffering from other diseases like acute respiratory distress, septicemia.
Serum glucose was analyzed using glucose oxidase from Aspergillus niger immobilized to alkylamine glass (pore diameter 55 nm) by the glutaraldehyde coupling method. The minimum detection limit was 3.6 mg/100 ml sample. The recovery of added glucose was 95%. A good correlation (r = 0.808) was found between glucose values obtained by a standard commercial method and the present method.
Trinder's method for glucose has nearly all the attributes of an ideal automated colorimetric glucose oxidase procedure. The chemicals used in the color reaction with peroxidase are readily available, the solutions are stable and can be prepared by the user, the method is highly specific and largely free of interferences, the sensitivity can be adjusted by the user to cover a wide range of glucose concentrations, and the reagents are not hazardous. We found very good agreement between results by this method and by the hexokinase and Beckman Glucose Analyzer methods. The method has been modified and adapted to the AutoAnalyzer I and SMA 6/60 (Technicon) with manifolds that give very little interaction between specimens. A study of the method by the simplex technique revealed that the glucose oxidase activity in the reagent is the most critical variable.
The comparative kinetic study of two glucose oxidizing enzymes, FAD-dependent glucose oxidase and PQQ-dependent glucose dehydrogenase, is presented in the artificial electron transfer mediator system based on ruthenium(III) compounds. It is demonstrated that FAD-dependent glucose oxidase and PQQ-dependent glucose dehydrogenase follow Michaelis kinetics in the D-glucose/ruthenium(III) system. PQQ-dependent glucose dehydrogenase is more active than FAD-dependent glucose oxidase in the process of D-glucose oxidation by ruthenium(III) compounds, this being due to the different catalytic mechanisms of these enzymes.
The purpose of this work was to evaluate the effectiveness of a new Membrane Electrochemical Reactor (MER) for the production of gluconic acid by glucose oxidase (GOD) catalysed glucose oxidation. The GOD was confined against the electrode surface with a dialysis membrane. The role of the electrochemical step was to eliminate by oxidation the hydrogen peroxide that appeared as a by-product of the reaction and strongly inhibited and/or inactivated GOD. The dialysis MER gave a transformation ratio of 30% with an initial glucose concentration of around 300 mM. This result is significantly better than the maximum of 10% obtained when hydrogen peroxide was eliminated by addition of a large excess of catalase in solution, as is generally done. The D-MER also revealed unexpected properties of the enzyme kinetics, such as an oscillatory behaviour, which were discussed.
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Glucose oxidase (beta-D-glucose:oxygen 1-oxidoreductase, EC 1.1.3.4) was immobilized in a crosslinked matrix of bovine serum albumin, catalase, glucose oxidase and glutaraldehyde on platinum foil. When placed in glucose solution, this enzyme-electrode elicited a potentiometric response that varied with the changes in glucose concentration. The immobilized glucose oxidase was present at 7.4-10.1 micrograms enzyme protein/ml of matrix, as determined with 125I-labelled enzyme. The coupled enzyme activity was stable over 120 h; however, the apparent activity of the immobilized glucose oxidase was markedly less than that for the same amount of enzyme free in solution. This indicated a significant level of diffusional resistance within the enzyme-matrix. The potentiometric response to glucose increased significantly as either the thickness of the enzyme-matrix or the glutaraldehyde content was reduced; this also was attributed to diffusional effects. Several enzyme-electrodes, constructed without exogenous catalase and with different amounts of glucose oxidase, showed greater sensitivity in potentiometric response at low glucose oxidase loadings. These results are consistent with the hypothesis that the potentiometric response arises from an interfacial reaction involving a hydrogen peroxide redox couple at a platinum surface. The data also suggest that an optimum range of hydrogen peroxide concentration exists for maximum electrode sensitivity.
Three glucose-oxidase (Diastix) and two copper-reduction (Clinitest) urine tests for glucose were compared to determine the differences in accuracy for various concentrations of glucose. Fifty volunteers were assigned on a random basis to one of five urine-testing methods and to a testing order for eight glucose samples. The samples were assayed spectrophotometrically to verify the actual concentrations of glucose, ranging form 0.1 to 20.0%. Scale points were assigned to correspond to the different glucose concentrations. The deviation of the volunteers' determinations above or below the actual concentrations were recorded as error points. A one-way analysis was conducted on the error points to determine it there were significant differences among the five testing methods. Significant differences were found among the five testing methods (p less than 0.01). The five-drop Clinitest method was significantly less accurate than the 1:5 Diastix and the two-drop Clinitest methods. Significant differences were found among the five testing methods at low and medium glucose concentrations but not at the high concentrations. In the glucose concentration range of 0.1-0.25%, the Diastix method with no dilution was significantly less accurate (p less than 0.01) than the two-drop Clinitest method. In the 0.5-1.25% range, the two-drop Clinitest was more accurate than Diastix 1:5, 1:10, and five-drop Clinitest. Overall, the two-drop Clinitest procedure was most accurate, particularly at the lower concentrations of glucose.
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Two automated glucose oxidase methods have been evaluated with respect to accuracy, precision, recovery, linearity and various potential interferences. Trinder's method on an AutoAnalyzer II had a between-day coefficient of variation (C.V.) of 2.6% (mean 228 mg/dl), was linear to 500 mg/dl, and produced a mean recovery of 99.7%. Comparison of Trinder's method with a manual, blanked hexokinase method yielded the regression equation: TR=--1.95 + HEX (1.04); Spearman's rho correlation coefficient was: 0.974. The Beckman System I glucose method had a between-day C.V. of 1.6% (mean 198 mg/dl), was linear to 500 mg/dl, and recovered an average of 98.0% of added glucose. Comparison with the same hexokinase method yielded: SYI = 1.27 + HEX (1.02: Spearman's rho = 0.991. None of the possible interfering compounds tested caused significant deviation of results by either method within the range of concentrations encountered physiologically. Trinder's method on the AutoAnalyzer II and the System I method are accurate, precise methods and are highly recommended for routine use in the clinical laboratory.