Sulfite Oxidase

Abstract

AbstractSulfite oxidase catalyzes the physiologically vital oxidation of sulfite to sulfate, the terminal reaction in the oxidative degradation of the sulfur‐containing amino acids, cysteine and methionine. It belongs to the molybdenum cofactor (Moco)‐containing family of enzymes that are characterized by the presence of a mononuclear Mo atom coordinated to the sulfur atoms of a pterin derivative, named molybdopterin. The homodimeric sulfite oxidase is located in the mitochondrial intermembrane space and each subunit contains a larger Moco‐containing domain and a smaller heme‐containing domain. Oxidation of sulfite to sulfate occurs at the molybdenum center with concomitant reduction of Mo(VI) to Mo(IV). Two electrons are singly transferred to theb5heme of the enzyme and from there to cytochromec. Sulfite oxidase deficiency results from defects either in the genes encoding proteins involved in molybdenum cofactor biosynthesis or in the sulfite oxidase gene itself. Several point mutations in the sulfite oxidase gene have been identified in patients with this disease worldwide. The crystal structure of wild‐type chicken sulfite oxidase provides the first atomic model for this enzyme and suggests possible reasons for how these substitutions interfere with catalysis or substrate binding.