MetaCyc Enzyme: 6-hydroxynicotinate reductase

Gene: hnr Accession Number: G-10435 (MetaCyc)

Species: Eubacterium barkeri

Subunit composition of 6-hydroxynicotinate reductase = [Hnr]4
         6-hydroxynicotinate reductase subunit = Hnr

6-Hydroxynicotinate reductase has been purified under anaerobic conditions from nicotinate-grown cells of Eubacterium barkeri. The enzyme is a homotetrameric [Fe-S] flavoprotein that contains up to 9.3 Fe and 6-8 acid-labile sulfur atoms per monomer. The flavin is covalently bound. [Alhapel06].
The apparent molecular mass of the subunit was determined by SDS-PAGE [Alhapel06] .

Molecular Weight of Polypeptide: 53.097 kD (from nucleotide sequence), 53.0 kD (experimental) [Alhapel06 ]

Unification Links: Protein Model Portal:Q0QLF7 , UniProt:Q0QLF7

Relationship Links: InterPro:IN-FAMILY:IPR017896 , InterPro:IN-FAMILY:IPR017900 , Pfam:IN-FAMILY:PF13237 , Prosite:IN-FAMILY:PS00198 , Prosite:IN-FAMILY:PS51379

Gene-Reaction Schematic: ?

Gene-Reaction Schematic

Enzymatic reaction of: 6-hydroxynicotinate reductase

Synonyms: 6-oxotetrahydronicotinate dehydrogenase, 6-hydroxynicotinic reductase

EC Number:

6-oxo-1,4,5,6-tetrahydronicotinate + 2 an oxidized ferredoxin <=> 6-hydroxynicotinate + 2 a reduced ferredoxin + 2 H+

The reaction direction shown, that is, A + B ↔ C + D versus C + D ↔ A + B, is in accordance with the Enzyme Commission system.

The reaction is favored in the opposite direction.

In Pathways: superpathway of nicotinate degradation , nicotinate degradation III

6-Hydroxynicotinate reductase catalyzes the reversible reduction of 6-hydroxynicotinic acid to the 4-5- dihydro derivative. It requires reduced ferredoxin as the electron donor in vivo. Reduced methyl viologen can serve as electron donor in vitro. The enzyme is unstable in the presence of air [Holcenberg69].

Regulators of Unknown Type: o-phenanthroline [Tsai71] , 2,2'-dipyridyl [Tsai71]

pH(opt): 6.5 [Holcenberg69]


Alhapel06: Alhapel A, Darley DJ, Wagener N, Eckel E, Elsner N, Pierik AJ (2006). "Molecular and functional analysis of nicotinate catabolism in Eubacterium barkeri." Proc Natl Acad Sci U S A 103(33);12341-6. PMID: 16894175

Holcenberg69: Holcenberg JS, Tsai L (1969). "Nicotinic acid metabolism. IV. Ferredoxin-dependent reduction of 6-hydroxynicotinic acid to 6-oxo-1,4,5,6-tetrahydronicotinic acid." J Biol Chem 244(5);1204-11. PMID: 5767303

Tsai71: Tsai L, Stadtman ER (1971). "Anaerobic degradation of nicotinic acid." Methods Enzymol. 18:233-249.

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Please cite the following article in publications resulting from the use of MetaCyc: Caspi et al, Nucleic Acids Research 42:D459-D471 2014
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