Enzyme from a sulphur-reducing bacterium. Molecular model of the enzyme aldehyde oxidoreductase from the Desulfovibrio gigas sulphur-reducing bacterium. An oxidoreductase is an enzyme that catalyses a redox (reduction and oxidation) reaction. The reduction of sulphur by the D. gigas bacterium is an example of a redox reaction. These bacteria have been studied for use in degrading radioactive waste, such as uranium compounds. Two types of models are shown here. The solid colours of the helical ribbons, arrows and sheets show the secondary structure (the shape of the enzyme), while the background tubular structure (faded colours) shows the molecule's chemical structure of 8121 atoms and their bonds.