© 2005 The Japanese Biochemical Society
BIOCHEMISTRY |
Thermococcus profundus 2-Ketoisovalerate Ferredoxin Oxidoreductase, a Key Enzyme in the Archaeal Energy-Producing Amino Acid Metabolic Pathway
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
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 (
ß
)2 consisting of four different subunits, = 45,000, ß = 31,000, = 22,000 and = 13,000, respectively. Electron paramagnetic resonance and resonance Raman spectra of the purified enzyme indicate the presence of approximately three [4Fe-4S] clusters per ß-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 (t1/2, approximately 5 min at 25°C), and is partly protected in the presence of magnesium ions, thiamine pyrophosphate and sodium chloride (t1/2, approximately 25 min at 25°C).
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