Rhodobacter sphaeroides denitrificans

Johnson, J.L., Bastian, N.R. Rajagopalan, K.V. (1990). Molybdop-terin guanine dinucleotide a modified form of molybdopterin identified in the molybdenum cofactor of dimethyl sulfoxide reductase from Rhodobacter sphaeroides forma specialis denitrificans. Proceedings of the National Academy of Sciences (USA) 87, 3190-4. 

Asymmetric synthesis of sulfoxides can be achieved by biocatalytic oxidation of sulfides and reduction of sulfoxides (Figure 33). i4-27s One example is the reduction of alkyl aryl sulfoxides by intact cells of Rhodobacter sphaeroides f.sp. denitrificans (Figure 33 (a)). 341 In the reduction of methyl -substituted phenyl sulfoxides, ( S )-cnanliomcrs were exclusively deoxygenated while enantiomerically pure (W)-isomcrs were recovered in good yield. For poor substrates such as ethyl phenyl sulfoxide, the repetition of the incubation after removing the toxic product was effective in enhancing the ee of recovered (f )-enantiomers to 100%. 

CcOs from bovine heart mitochondria and bacteria Rhodobacter sphaeroides and Paracoccus denitrificans) have been determined, culminating in the 2.0 A resolution structure of CcO from Rhodobacter sphaeroides which contains only the two catalytic subunits — subunit I with 3 redox-active centres, haem a, and the catalytic site made up of haem ag and Cub, and subunit II with the Cua redox centre made up of 2 copper ions, together with two other subunits (Qin, Hiser, Mulichak, Garavito, Ferguson-Miller, 2006). 

There are two main types of NiRs involved in the reduction of nitrites, namely, the heme-containing cytochrome cdj NiR which was obtained and first purified from Thiosphaera pantotropha (261). The second kind of NiR is the copper-containing NiR which was first isolated from Alcaligenes xylosoxidans NCIB 11015, a bacterial isolated from a soil in Japan. Other Cu NiR have been isolated from, Achromohacter cycloclastes, Alcaligenes faecalis S-6, Bacillus halodenitrificans, Haloferax denitrificans, Nitrosomonas europaea, Pseudomonas aureofaciens, Rhodobacter sphaeroides, and Hyphomicrobium sp. (262 and references thereinj. In mammalian systems, nitrites are reduced by deoxyHb (263) and by ferrous myoglobin (264,265) to nitric oxide. In synthetic iron porphyrins. Ford and coworkers have demonstrated how nitrites inhibit the reductive nitrosylation process by forming ferric-nitrites species (266). 

A selection of biocatalytic deoxygenation reactions is shovm in Figure 1.8. The reducing power of baker s yeast in an ethanol-water mixture and sodium hydroxide at 60° C has been found effective for the rapid and selective reduction of a series of N-oxides like aromatic and heteroaromatic N-oxide compounds [118]. DMSO reductase from Rhodobacter sphaeroides f sp. denitrificans catalyzed the (S)-enantioselective reduction of various sulfoxides and enabled the resolution of racemic sulfoxides for the synthesis of (R)-sulfoxides with >97% ee [119,120]. Purified dimethyl sulfoxide reductase from Rhodobacter capsulatus resolved a racemic mixture of methyl p-tolyl sulfoxide by catalyzing the reduction of (S)-methyl p-tolyl sulfoxide and gave enantio-merically pure (J )-methyl p-tolyl sulfoxide in 88% yield, while whole cells of E. coli,... 

Abo, M., Tachibana, M., Okubo, A., and Yamazaki, S. (1995) Enantioselective deoxygenation of alkyl aryl sulfoxides by DM SO reductase from Rhodobacter sphaeroides f s. denitrificans. Bioorg. Med. Chem., 3,109-112. 

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