Sulphite dehydrogenase

Sulphite dehydrogenase, 1.8.2.1 Mo-pterin, Heme c Sulphide PG/DDAB [122]... 

Of the mammalian enzymes, the sulphite oxidase of bovine liver has only recently been discovered to contain molybdenum (15). The better known molybdenum enzymes, xanthine oxidase from cows milk (31) and aldehyde oxidase from rabbit liver (16) are closely related to one another as they are to the xanthine dehydrogenases from chicken liver (17) and from bacteria (18). 

Fig. 3.1. A, The respiratory chain. Q and c stand for ubiquinone and cytochrome c, respectively. Auxiliary enzymes that reduce ubiquinone include succinate dehydrogenase (Complex II), a-glycerophosphate dehydrogenase and the electron-transferring flavoprotein (ETF) of fatty acid oxidation. Auxiliary enzymes that reduce cytochrome c include sulphite oxidase. B, Thermodynamic view of the respiratory chain in the resting state (State 4). Approximate values are calculated according to the Nernst equation using oxidoreduction states from work by Muraoka and Slater, (NAD, Q, cytochromes c c, and a oxidation of succinate [6]), and Wilson and Erecinska (b-562 and b-566 [7]). The NAD, Q, cytochrome b-562 and oxygen/water couples are assumed to equilibrate protonically with the M phase at pH 8 [7,8]. E j (A ,/ApH) for NAD, Q, 6-562, and oxygen/water are taken as —320 mV ( — 30 mV/pH), 66 mV (- 60 mV/pH), 40 mV (- 60 mV/pH), and 800 mV (- 60 mV/pH) [7-10]. FMN and the FeS centres of Complex I (except N-2) are assumed to be in redox equilibrium with the NAD/NADH couple, FeS(N-2) with ubiquinone [11], and cytochrome c, and the Rieske FeS centre with cytochrome c [10]. The position of cytochrome a in the figure stems from its redox state [6] and its apparent effective E -, 285 mV in...

Heme Cytochrome c Cytochrome c oxidase, cytochrome c peroxidase, cellobiose dehydrogenase, nitrate reductase, sulphite oxidase, theophylline oxidase, cytochrome 62... 

Molybdenum cofactor deficiency (MoCoD) is an autosomal recessive, fatal neurological disorder, characterized by the combined deficiency of sulphite oxidase, xanthine dehydrogenase, and aldehyde oxidase. No therapy is known for this rare disease, which results in neonatal seizures and other neurological symptoms identical to sulfite oxidase deficiency. Heterozygous carriers of a MoCo deficiency allele do not display any symptoms (Reiss et al. 1999). 

Another important naturally occurring pteridine is molybdopterin, apparently (9.28), which is the coenzyme of xanthine dehydrogenase, aldehyde oxidase, nitrate reductase, sulphite oxidase and presumably other enzymes that need both molybdenum and iron to function (Johnson and Rajagopolan, 1982). Xanthopterin, a co-lymphokine (p. 182), inhibits proliferation of lymphocytes (Ziegler 1983). 

Molybdenmn Xanthine dehydrogenase Sulphite oxidase Purine metabolism Sulphite oxidation... 

The biochemistry of this redirection of the ethanol fermentation is quite simple. The sulphite forms a condensation product with acetaldehyde, which is normally the immediate precursor of ethanol. This cannot be reduced by alcohol dehydrogenase, and the cell must find an alternative route to reoxidize NADH. It does this by reducing dihydroxyacetone phosphate, and after hydrolysis of the phosphate ester, glycerol is excreted (Figure 6.2). This manipulation of the yeast s metabolism, the details of which were not then understood, allowed a minor fermentation product to become the major one. 

Table 23.3. Xanthine dehydrogenase (XDH)/sulphite oxidase SO)/aldehyde oxidase (AO) deficiencies ...

Molybdenum-oxo-transferases e.g. xanthine dehydrogenase sulphite oxidase... 

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