Sulfite oxidase (EC 1.8.3.1) is an enzyme in the mitochondria of all eukaryotes, with exception of the yeasts. It oxidizes sulfite to sulfate and, via cytochrome c, transfers the electrons produced to the electron transport chain, allowing generation of ATP in oxidative phosphorylation. This is the last step in the metabolism of sulfur-containing compounds and the sulfate is excreted. Sulfite oxidase is a metallo-enzyme that utilizes a molybdopterin cofactor and a heme group (in a case of animals). It is one of the cytochromes b5 and belongs to the enzyme super-family of molybdenum oxotransferases that also includes DMSO reductase, xanthine oxidase, and nitrite reductase. In mammals, the expression levels of sulfite oxidase is high in the liver, kidney, and heart, and very low in spleen, brain, skeletal muscle, and blood. Structure
As a homodimer, sulfite oxidase contains two identical subunits with an N-terminal domain and a C-terminal domain. These two domains are connected by ten amino acids forming a loop. The N-terminal domain has a heme cofactor with three adjacent antiparallel beta sheets and five alpha helices. The C-terminal domain hosts a molybdopterin cofactor that is surrounded by thirteen beta sheets and three alpha helices. The molybdopterin cofactor has a Mo(VI) center, which is bonded to a sulfur from cysteine, an ene-dithiolate from pyranopterin, and two terminal oxygens. It is at this molybdenum center that the catalytic oxidation of sulfite takes place. The pyranopterin ligand which coordinates the molybdenum centre via the enedithiolate.
Without proper treatment a permanent deformity of the finger may occur. Diagnosis
The diagnosis is generally based on symptoms and supported by X-rays. The injury can be accompanied by swelling and ecchymosis. Treatment
The management goal is to restore extension of the joint. Treatment is generally with a splint that holds the first joint of the finger straight continuously for 8 weeks. This should begin within a week of the injury. The splint may be worn just at night for a few additional weeks after this. The splint acts to immobilize flexing of the joint. Surgery generally does not improve outcomes. It may be required if the finger cannot be straightened by pushing on it or the break has pulled off more than 30% of the joint surface. Surgery may be preferred over the use of a split if a child is non-compliant. If the problem has been present a long time surgery may also be required. An open fracture may be another reason. Surgery will put the finger in a neutral position and drill a wire through the distal interphalangeal joint (DIP) to the proximal interphalangeal joint (PIP), forcing immobilization. See also
Busch fracture
Jersey finger

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