Purification and properties of sulfite oxidase from different sources: a mini review

Sulfite oxidase (SOx) (EC 1.8.3.1) is found in the mitochondria of all eukaryotes. It oxidizes sulfite to sulfate and via cytochrome c. It transfers the electrons produced to the electron transport chain (ETC), allowing generation of ATP by oxidative phosphorylation. This is the last step in the metabolism of sulfur-containing compounds and the sulfate is excreted. SOx is a metallo-enzyme containing a molybdopterin cofactor and a heme group. It is one of the cytochrome b5 and belongs to the enzyme super-family of molybdenum oxotransferases that also includes dimethylsulfoxide (DMSO) reductase, xanthine oxidase and nitrite reductase. In mammals, the expression level of SOX is high in the liver, kidney and heart but very low in spleen, brain, skeletal muscle and blood1–3 of functional SOx causes sulfite deficiency. This causes neurological disorders, mental retardation, physical deformities, dislocated lenses, degradation of brain and early death thus sulfite level in body must normally be strictly maintained. SOx was first isolated from bovine liver and subsequently also purified from animal sources such as rat, dog, beef, humans, chicken and goat liver and plant sources such as Spinacia oleracea, Malva sylvestris, Nicotiana tabacum and Arabidopsis thaliana (Table 1).4 The present review deals with the distribution, purification, and characterization of SOX from various sources.