A hyperactive NAD(P)H : rubredoxin oxidoreductase from the hyperthermophilic archaeon Pyrococcus furiosus

NAD(P)H:rubredoxin oxidoreductase (NROR) has been purified from the hyperth ermophilic archaeon Pyrococcus furiosus. The enzyme is exceedingly active i n catalyzing the NADPH dependent reduction of rubre doxin, a small (5.3-kDa ) iron-containing redox protein that had previously been purified from this organism. The apparent V-max at 80 degrees C is 20,000 mu mol/min/mg, whic h corresponds to a k(cat)/K-m value of 300,000 mM(-1) s(-1). The apparent K -m values measured at 80 degrees C and pH 8.0 for rubredoxin, NADPH, and NA DH were 50, 5, and 34 mu M, respectively. The enzyme did not reduce P. furi osus ferredoxin. NROR is a monomer with a molecular mass of 45 kDa and cont ains one flavin adenine dinucleotide molecule per mole but lacks metals and inorganic sulfide. The possible physiological role of this hyperactive enz yme is discussed.