Thermococcus profundus 2-Ketoisovalerate Ferredoxin Oxidoreductase, a Key Enzyme in the Archaeal Energy-Producing Amino Acid Metabolic Pathway

Authors: Ozawa, Yukiko¹; Nakamura, Takahiro¹; Kamata, Natsu¹; Yasujima, Daisuke¹; Urushiyama, Akio²; Yamakura, Fumiyuki³; Ohmori, Daijiro³; Imai, Takeo¹

Source: The Journal of Biochemistry, Volume 137, Number 1, January 2005 , pp. 101-107(7)

Publisher: Oxford University Press

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Abstract:

2-Ketoisovalerate ferredoxin oxidoreductase (VOR) is a key enzyme in hyperthermophiles catalyzing the coenzyme A–dependent oxidative decarboxylation of mainly aliphatic amino acid–derived 2-keto acids. The very oxygen-labile enzyme purified under anaerobic conditions from a hyperthermophilic archaeon, Thermococcus profundus, is a hetero-octamer ( alpha

)<inf>2</inf> consisting of four different subunits, alpha

= 45,000,

= 31,000,

= 22,000 and delta

= 13,000, respectively. Electron paramagnetic resonance and resonance Raman spectra of the purified enzyme indicate the presence of approximately three [4Fe-4S] clusters per alpha

-protomer, although one of the clusters has a tendency to be converted to a [3Fe-4S] form during purification. The optimal temperature for the enzyme activity is 93 ± 2°C and the cognate [4Fe-4S] ferredoxin serves as an electron acceptor of the enzyme. The purified enzyme is highly oxygen-labile (t<inf>1/2</inf>, approximately 5 min at 25°C), and is partly protected in the presence of magnesium ions, thiamine pyrophosphate and sodium chloride (t<inf>1/2</inf>, approximately 25 min at 25°C).

Document Type: Research article

DOI: http://dx.doi.org/10.1093/jb/mvi012

Affiliations: 1: Department of Life Science and Graduate School of Life Science, and 2: Department of Chemistry and Graduate School of Chemistry, Rikkyo (St. Paul’s) University, Toshima-ku, Tokyo 171-8501; and 3: Department of Chemistry, Juntendo University School of Medicine, Inba, Chiba 270-1695

Publication date: 2005-01-01