|Gene:||xdh||Accession Number: G-12655 (MetaCyc)|
Synonyms: rrnAC3034, gfo6
Species: Haloarcula marismortui
Subunit composition of
D-xylose dehydrogenase = [Xdh]4
D-xylose dehydrogenase subunit = Xdh
The native complex apparent molecular mass was determined to be 175 kDa by gel filtration chromatography and the enzyme was proposed to be a homotetramer [Johnsen04].
The enzyme was induced upon growth of cells on α-D-xylopyranose (D-xylose). Native enzyme was purified from cell extracts. Recombinant enzyme was expressed in inclusion bodies in Escherichia coli. It was activated by denaturation in urea followed by refolding in the presence of salts, glutathione and substrates, with subsequent purification and characterization [Johnsen04].
The native subunit apparent molecular mass was determined by SDS-PAGE to be 57 kDa. The discrepancy with the calculated molecular mass of 39.9 kDa is common in halophilic proteins [Johnsen04].
|Map Position: [2,693,010 <- 2,694,092]|
Molecular Weight of Polypeptide: 39.937 kD (from nucleotide sequence), 57.0 kD (experimental) [Johnsen04 ]
Molecular Weight of Multimer: 175.0 kD (experimental) [Johnsen04]
Enzymatic reaction of: D-xylose dehydrogenase
EC Number: 18.104.22.168
The reaction direction shown, that is, A + B ↔ C + D versus C + D ↔ A + B, is in accordance with the direction in which it was curated.
This reaction is reversible.
Kinetic parameters are for the native enzyme purified from cell extracts (the apparent Vmax of the recombinant enzyme was approximately 40% lower). The enzyme utilized both NADP+ and NAD+ as cosubstrate but had a 6-fold higher apparent Km for NAD+ indicating that NADP+ is the physiological electron acceptor [Johnsen04].
This enzyme efficiently utilized both α-D-xylopyranose and D-ribose as substrate but the highest catalytic efficiency was obtained using α-D-xylopyranose and NADP+. D-glucose showed a 70-fold lower catalytic efficiency and D-galactose was even less efficient as a substrate. D-arabinose and D-fructose were not significantly oxidized [Johnsen04].
This halophilic enzyme was strongly stimulated by 1.5 M potassium chloride, 1.5 M sodium chloride, or 100 mM MgCl2 The rate dependence on pH and temperature was assayed in the presence of 1.5 M potassium chloride [Johnsen04].
T(opt): 50 °C [Johnsen04]
pH(opt): 8.3 [Johnsen04]
Drew98: Drew KN, Zajicek J, Bondo G, Bose B, Serianni AS (1998). "13C-labeled aldopentoses: detection and quantitation of cyclic and acyclic forms by heteronuclear 1D and 2D NMR spectroscopy." Carbohydrate Research 307(3-4);199-209.
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