Starkeya novella

Kelly DP, McDonald IR, Wood AP. 2000. Proposal for the reclassification of Thiobacillus novellus as Starkeya novella gen. nov., comb, nov., in the a-subclass of the Proteobacteria. Int J Syst Evol Microbiol 50 1797-802. 

Starkeya novella Soil microbe Label-free Metabolic pathway analysis (209)... 

Sulfite dehydrogenase Starkeya novella afi, 50 Mo02(SCys)(MPT) heme c S03 " — S04 " ... 

Kappler U., Friedrich C. G., Truper H. G., and Dahl C. (2001) Evidence for two pathways of thiosulfate oxidation in Starkeya novella (formerly Thiobacillus novellas). Arch. Microbiol. 175, 102-111. 

The affinity to carbon monoxide (CO) of the oxidase is very low as compared to other cytochromes c oxidase though the oxidase binds completely with carbon monoxide in 100% carbon monoxide atmosphere, its CO-complex dissociates easily to the oxidase and carbon monoxide in air unlike other cytochromes c oxidase (Erickson et al., 1972 Yamazaki et al., 1985) except for Starkeya novella cytochrome c oxidase monomer, which does not bind with carbon monoxide bubbled in air (Shoji et al., 1992). 

In Starkeya novella, sulfite is oxidized to sulfate by the catalysis of sulfite-cytochrome c oxidoreductase [reaction (4.5)]. The enzyme catalyzes the reduction with sulfite of not only native ferricytochrome c-550 but also horse ferricytochrome c and ferricyanide (Charles and Suzuki, 1966b Yamanaka et al., 1971, 1981b). The enzyme with a molecular mass of 40 kDa has a cytochrome c-551 subunit (23 kDa) (Yamanaka et al., 1981b) and molybdenum (Toghrol and Southerland, 1983). Recently, Kappler et al. (2000) has reported that the molecular mass of the enzyme is 46 kDa and has cytochrome c subunit of 8.8 kDa. 

Starkeya novella cytochrome c-550 was first partially purified by Charles and Suzuki (1966b), and thereafter highly purified by Yamanaka et al. (1971, 1991b). The cytochrome functions as the electron acceptor for sulfite-cytochrome c oxidoreductase as mentioned above, and as the electron donor for cytochrome c oxidase (Yamanaka and Fujii, 1980). It resembles mitochondrial cytochrome c in that it... 

Starkeya novella cytochrome c oxidase reacts rapidly not only with native cytochrome c but also with tuna and yeast cytochromes c, while it reacts very slowly with horse and cow cytochromes c (Yamanaka and Fukumori, 1977 Yamanaka and Fujii, 1980). Cytochromes c which react rapidly with the oxidase have Tyr (46), while cytochromes c which react slowly with the oxidase have Phe (46) (Yamanaka and Fukumori, 1978). Thus, human cytochrome c reacts with the oxidase more rapidly than horse and cow cytochromes c. However, native cytochrome c which reacts rapidly with the oxidase has Phe(46). 

Cytochrome c oxidase of Acidithiobacillus ferrooxidans was previously called cytochrome a1( as it shows the a peak at 595 nm (Ingledew, 1982). However, as the oxidase purified from the bacterium has two heme A molecules and two copper atoms in the minimal functional unit and one of the two molecules of heme A combines with carbon monoxide, it is a cytochrome aa3-type cytochrome c oxidase although it has the a peak at 595 nm (Kai et al., 1992). It differs from the usual cytochrome aa3 in having only one molecule of heme A and one atom of copper in the minimal structural unit, which comprises one molecule each of three kinds of subunits (54 kDa, 21 kDa, 15 kDa) like Starkeya novella cytochrome c oxidase (Shoji et al., 1992). [The DNA study suggests the presence of four subunits with the molecular masses of 69, 28, 18 and 6.4 kDa (Appia-Ayme et al., 1999)]. The minimal functional unit of the A. ferrooxidans oxidase is a dimer of the minimal structural unit, and the dimer shows general properties of cytochrome ach except that the a peak is present at a wavelength shorter than 600 nm of the absorption spectrum. The oxidase resembles Nitrosomonas europaea cytochrome c oxidase (Yamazaki et al., 1985) (see pp. 25-26) in the position of the a peak of the absorption spectrum. 

There is considerable structural diversity amongst the bacterial sulfite oxidizing enzymes. The two most studied bacterial SDH enzymes have been isolated from the soil bacteria Starkeya novella, SorAB, a heterodimer bearing both a Mo and heme-containing subunit, and Sinorhizobium meliloti, SorT, which only has a Mo cofactor but donates electrons to an independent cytochrome (SorU). Neither enzyme shows significant oxidase activity. 

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