Sulfur oxidizing dioxygenases

There are three dioxygenases that oxidize sulfur. 

Despite the similar funetions of the preeeding enzymes, they may well make use of dilferent meehanisms 1, 2). Although all require iron, eysteine dioxygenase requires the ferrous state and NADPH 220), whereas eysteamine dioxygenase uses high-spin ferrie ion in the aetual eatalysis 219). The faet that the E.P.R. speetrum of the last enzyme is modified by addition of the substrate, namely eysteamine, under anaerobie eonditions 219) demonstrates that it is the substrate whieh interaets with the metal eo-faetor. 

This enzyme eontains one gram atom of ferrous ion per mole of enzyme and has a speeifie requirement for eysteine 123, 223—225). 

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The possible roles in sulfur (and sulfide or sulfane-) oxidation of a sulfur dioxygenase or of electron-transport-linked hydration/dehydrogenation are outlined above, but the fate of the sulfite product may be more complex than previously considered. Vishniac and Santer (1957) showed that S-labeled sulfide was rapidly oxidized first to thiosulfate (and polythionates) and then to sulfate by T. thioparus. This observation was incorporated into the original Peck scheme (Eqs. 15.13-15.17) by Peck and Fisher (1962), who realized that the complete oxidation of thiosulfate (after reductive scission to sulfite and sulfide Eq. 15.3) could be explained if there was recycling of sulfide to produce thiosulfate ... 

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