Sulfite oxidase

Sulfite oxidase (SO) is a critical enzyme in the metabolism of sulfur-containing amino acids. It catalyzes the oxidation of sulfite to sulfate, a reaction that is essential for the detoxification of sulfite, which is potentially toxic if accumulated in the body. This enzyme plays a pivotal role in the amino acid metabolism pathway, particularly in the catabolism of methionine and cysteine.

Function

Sulfite oxidase is a molybdenum-containing enzyme that is located in the mitochondria. It is involved in the final step of the degradation of sulfur amino acids, where it oxidizes sulfite (\(SO_3^{2-}\)) to sulfate (\(SO_4^{2-}\)). This reaction is not only crucial for the detoxification of sulfite but also for the production of sulfate, which is necessary for the synthesis of sulfur-containing compounds, such as glutathione, taurine, and heparan sulfate.

Structure

The enzyme is a dimer, with each monomer consisting of a molybdenum cofactor (MoCo) domain and a heme domain. The MoCo domain is responsible for the oxidation of sulfite to sulfate, while the heme domain transfers electrons from sulfite to the final electron acceptor, which is usually cytochrome c or oxygen.

Clinical Significance

Mutations in the SUOX gene, which encodes sulfite oxidase, can lead to sulfite oxidase deficiency. This rare genetic disorder is characterized by severe neurological abnormalities, dislocated lenses, and early death. The absence of functional sulfite oxidase leads to the accumulation of toxic levels of sulfite, which can damage various tissues, especially the brain.

Diagnosis and Treatment

Diagnosis of sulfite oxidase deficiency typically involves biochemical tests to measure the levels of sulfite, sulfate, and S-sulfocysteine in urine. Genetic testing can confirm mutations in the SUOX gene. Currently, there is no cure for sulfite oxidase deficiency, and treatment is supportive, focusing on managing symptoms and preventing complications.

See Also

• Molybdenum cofactor deficiency
• Metabolic disorder
• Amino acid metabolism