Glucose Oxidase from Aspergillus niger

Molecular Weight: 160 kDa (gel filtration)
pI: 4.2
Extinction coefficient: E^1% = 16.7 (280 nm)

Glucose oxidase from Aspergillus niger is a dimer consisting of 2 equal subunits with a molecular mass of 80 kDa each. Each subunit contains one flavin adenine dinulceotide moiety and one iron. The enzyme is a glycoprotein containing ~16% neutral sugar and 2% amino sugars. The enzyme also contains 3 cysteine residues and 8 potential sites for N-linked glycosylation.

Glucose oxidase is capable of oxidizing D-aldohexoses, monodeoxy-D-glucoses, and methyl-D-glucoses at varying rates.

The pH optimum for glucose oxidase is 5.5, while it has a broad activity range of pH 4-7. Glucose oxidase is specific for β-D-glucose with a K_M of 33-110 mM.

Glucose oxidase does not require any activators, but it is inhibited by Ag⁺, Hg²⁺, Cu²⁺, phenylmercuric acetate, and p-chloromercuribenzoate. It is not inhibited by the nonmetallic SH reagents: N-ethylmaleimide, iodoacetate, and iodoacetamide.

Glucose oxidase can be utilized in the enzymatic determination of D-glucose in solution. As glucose oxidase oxidizes β-D-glucose to D-gluconolactate and hydrogen peroxide, horseradish peroxidase is often used as the coupling enzyme for glucose determination. Although glucose oxidase is specific for β-D-glucose, solutions of D-glucose can be quantified as α-D-glucose will mutorotate to β-D-glucose as the β-D-glucose is consumed by the enzymatic reaction.

Glucose oxidase is widely used in the food and pharmaceutical industries as well as a major component of glucose biosensors.

Glucose oxidase catalyses the oxidation of β-d-glucose to d-glucono-β-lactone and hydrogen peroxide, with molecular oxygen as an electron acceptor.

Crude. May contain catalase, amylase, maltase, glycogenase, invertase, and galactose oxidase.

Protein determined by biuret.

One unit will oxidize 1.0 μmole of β-D-glucose to D-gluconolactone and H₂O₂ per min at pH 5.1 at 35 °C, equivalent to an O₂ uptake of 22.4 μl per min. If the reaction mixture is saturated with oxygen, the activity may increase by up to 100%.