Pyrococcus furiosus glyceraldehyde 3-phosphate oxidoreductase has comparable W6+/5+ and W5+/4+ reduction potentials and unusual [4Fe-4S] EPR properties

Pyrococcus furious glyceraldehyde 3-phosphate oxidoreductase has been chara cterized using EPR-monitored redox titrations. Two different W signals were found. W-i(5+) is an intermediate species in the catalytic cycle, with the midpoint potentials E-m(W6+/5+) = -507 mV and E-m(W5+/4+) = -491 mV, W-2(5 +) represents an inactivated species with E-m (W6+/5+) = -329 mV, The cuban e cluster exhibits both S = 3/2 and S = 1/2 signals with the same midpoint potential: E-m([4Fe-4S](2+/1+)) = -335 mV, The S = 1/2 EPR signal is unusua l with all g values below 2.0. The titration results combined with catalyti c voltammetry data are consistent with electron transfer from glyceraldehyd e 3-phosphate first to the tungsten center, then to the cubane cluster and finally to the ferredoxin, (C) 1999 Federation of European Biochemical Soci eties.