Glucose Oxidase

Glucose oxidase (ß -?D-glucose:oxygen 1-oxidoreductase, EC1.1.3.4) catalyses the oxidation of ß-D-glucose to D-glucono-1,5-lactone and hydrogen peroxide, using molecular oxygen as the electron acceptor.

Glucose oxidase is widely used for the determination of glucose in body fluids and in removing residual glucose and oxygen from beverages and foodstuffs. Furthermore, Glucose oxidase-producing moulds such as Aspergillus and Penicillum Species are used for the biological production of gluconic acid.

The Glucose oxidase enzyme (GOx) (EC 1.1.3.4) binds to beta-D-glucose (an isomer of the six carbon sugar, glucose) and aids in breaking the sugar down into its metabolites. GOx is a dimeric protein which catalyzes the oxidation of beta-D-glucose into D-glucono-1,5-lactone which then hydrolyzes to gluconic acid.

In order to work as a catalyst, GOx requires a cofactor, flavin adenine dinucleotide (FAD). FAD is a common component in biological oxidation-reduction (redox reactions). Redox reactions involve a gain or loss of electrons from a molecule. In the GOx catalyzed redox reaction, FAD works as the initial electron acceptor and is reduced to FADH2. Then FADH2 is oxidized by the final electron acceptor, molecular oxygen (O2) which can do so because it has a higher reduction potential. O2 is then reduced to hydrogen peroxide (H2O2).

The glucose oxidase enzyme is commonly used in biosensors to detect levels of glucose by keeping track of the number of electrons passed through the enzyme by connecting it to an electrode and measuring the resulting charge. This has a possible application in the world of nanotechnology when used in conjuntion with tiny electrodes as glucose sensors for diabetics.

Glucose oxidase, a flavoenzyme, catalyzes the following reaction:

Bright and Porter (1975) have reviewed the kinetic behavior and redox states of the flavin coenzyme. Bentley (1963) has reviewed the general properties of the enzyme.

Since its discovery as an "antibiotic" (shown subsequently to be due to peroxide formation) there has been an interest in glucose oxidase, chiefly because of its utility in glucose estimation. Following Keston's report in 1956 of coupling the reaction to peroxidase and a chromogen, (qualitative) glucose "dip-sticks" became available for screening for urine glucose. Based on Teller's paper in the same year, Worthington offered the first quantitative enzymatic system for the colorimetric determination of glucose.

Glucose oxidase usually occurs as a glycoprotein, with a mannose-type carbohydrate content of around 16%. However, different forms of the enzyme have been isolated, including a non-glycosylated enzyme from the fungus Phanerochaete chrysosporium. Glucose oxidase is secreted by the fungus, and is distributed between the extracellular fluid surrounding the mould, the cell wall, and in the slime mucilage. The synthesis of glucose oxidase can be induced by various substances, including molecular oxygen, which induces the transcription of the enzyme.

Bright and Porter (1975) have reviewed the kinetic behavior and redox states of the flavin coenzyme. Bentley (1963) has reviewed the general properties of the enzyme.

Since its discovery as an "antibiotic" (shown subsequently to be due to peroxide formation) there has been an interest in glucose oxidase, chiefly because of its utility in glucose estimation. Following Keston's report in 1956 of coupling the reaction to peroxidase and a chromogen, (qualitative) glucose "dip-sticks" became available for screening for urine glucose. Based on Teller's paper in the same year, Worthington offered the first quantitative enzymatic system for the colorimetric determination of glucose.

Glucose oxidase usually occurs as a glycoprotein, with a mannose-type carbohydrate content of around 16%. However, different forms of the enzyme have been isolated, including a non-glycosylated enzyme from the fungus Phanerochaete chrysosporium. Glucose oxidase is secreted by the fungus, and is distributed between the extracellular fluid surrounding the mould, the cell wall, and in the slime mucilage. The synthesis of glucose oxidase can be induced by various substances, including molecular oxygen, which induces the transcription of the enzyme.