Johnson J L, Rajagopalan K V
Ciba Found Symp. 1979(72):119-33. doi: 10.1002/9780470720554.ch8.
In animals the terminal step in the pathway for degradation of sulphur-containing amino acids is the oxidation of sulphite to sulphate. This reaction is catalysed by the enzyme sulphite oxidase. The enzyme contains molybdenum and a cytochrome b5 type haem, is localized in the mitochondrial intermembrane space and transfers electrons from sulphite to cytochrome c on the inner membrane. The sulphite oxidase protein has a molecular weight of 110 000 (chicken) to 122 000 (human) and exists as a dimer of identical subunits. The haem and molybdenum cofactors are present on separate domains of the molecule. The structure of the molydbenum cofactor has not been worked out in detail, but this cofactor is known to be present in many other molybdoenzymes including xanthine oxidase and nitrate reductase. Three cases of genetic sulphite oxidase deficiency in humans have been reported. The three affected children displayed mental retardation, neurological abnormalities and dislocated ocular lenses. The biochemical basis for lack of enzyme activity in each case has been studied. All three have been shown to lack the sulphite oxidase protein, but in one case this appears to be secondary to a defect in synthesis of the molybdenum cofactor. Sulphite oxidase deficiency has been produced in the rat by administration of high levels of tungsten. Sulphite oxidase-deficient animals are particularly susceptible to the toxic effects of sulphite and atmospheric sulphur dioxide.
在动物体内，含硫氨基酸降解途径的最后一步是亚硫酸盐氧化为硫酸盐。此反应由亚硫酸盐氧化酶催化。该酶含有钼和细胞色素b5型血红素，定位于线粒体外膜间隙，可将电子从亚硫酸盐传递至内膜上的细胞色素c。亚硫酸盐氧化酶蛋白的分子量在110000（鸡）至122000（人）之间，以相同亚基的二聚体形式存在。血红素和钼辅因子存在于分子的不同结构域。钼辅因子的结构尚未详细阐明，但已知该辅因子存在于许多其他钼酶中，包括黄嘌呤氧化酶和硝酸还原酶。据报道，人类中有3例遗传性亚硫酸盐氧化酶缺乏症。这3名患病儿童均表现出智力发育迟缓、神经异常和晶状体脱位。对每例缺乏酶活性的生化基础进行了研究。结果表明，3例均缺乏亚硫酸盐氧化酶蛋白，但其中1例似乎继发于钼辅因子合成缺陷。通过给大鼠喂食高剂量的钨可导致其亚硫酸盐氧化酶缺乏。缺乏亚硫酸盐氧化酶的动物对亚硫酸盐和大气中的二氧化硫的毒性作用尤为敏感。
