Oxidase is an enzyme, which is involved in an oxidation-reduction reaction. Oxidase plays a catalytic role and is particularly important in reactions that feature dioxygen (O2) as an electron acceptor. Oxidase enzymes are a subclass of the oxidoreductases family. Oxidoreductase enzymes catalyse the transportation of electrons from a molecule, known as the reductant or the electron donor, to the oxidant or electron acceptor.
When oxidase plays a role in a reaction, which involves donating an atom of hydrogen, oxygen becomes water (H2O) or hydrogen peroxide (H2O2). In some cases, reactions, for example those that feature xanthine oxidase or monoamine oxidase, do not involve free oxygen molecules.
One of the most important oxidase enzymes is cytochrome C oxidase. This enzyme plays a critical role in enabling the body to utilise oxygen in the production of energy, and it is also the last enzyme in the final stage of the respiratory electron transfer chain. The enzyme takes an electron from each of the four cytochrome C molecules and converts them to a dioxygen molecule, which then turns the molecular oxygen into two water molecules. This process is part of ATP synthesis.
The primary function of oxidase is to catalyse oxidation, a chemical reaction, which involves moving electrons. One of the most important examples of oxidase function is the role played by cytochrome C oxidase in food oxidation. This enzyme is responsible for regulating the final step to create water by taking the remaining electrons, and adding them to oxygen and hydrogen ions. This process facilitates the creation of a substantial amount of energy. In the world at large, the combination of hydrogen and oxygen can be explosive, but within the cells, the reaction is carefully monitored by the cytochrome C oxidase enzyme.
An oxidase test is used to determine whether bacteria produce cytochrome C oxidase and is therefore involved in the electron transport chain. If a bacterium does produce cytochrome C oxidase, the enzyme will oxidise the reagent used in the test (usually tetramethyl-p-phenylenediamine) to produce a purple colour. If the bacterium doesn’t produce cytochrome C oxidase, no colour change will take place. A positive test result indicates that a bacterium is aerobic and can therefore use oxygen for respiration.
The oxidase test can be used to identify specific strains of bacteria and differentiate between species.
The structure of oxidase enzymes varies. To use an example, the complex structure of cytochrome C oxidase comprises a large membrane, which contains a host of metal components and 14 protein subunits. In mammals, 11 of the subunits originate in the nucleus, with the remaining three units synthesised within the mitochondria. The complex consists of two hemes (cytochrome A and cytochrome A3) and two copper centres, CUA and CUB.