Pyrococcus furiosus glyceraldehyde 3-phosphate oxidoreductase has comparable W 6+/5+ and W 5+/4+ reduction potentials and unusual [4Fe-4S] EPR properties

Abstract

Pyrococcus furiosus glyceraldehyde 3-phosphate oxidoreductase has been characterized using EPR-monitored redox titrations. Two different W signals were found. W 1 5+ is an intermediate species in the catalytic cycle, with the midpoint potentials E m(W 6+/5+)=−507 mV and E m(W 5+/4+)=−491 mV. W 2 5+ represents an inactivated species with E m(W 6+/5+)=−329 mV. The cubane 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 unusual with all g values below 2.0. The titration results combined with catalytic voltammetry data are consistent with electron transfer from glyceraldehyde 3-phosphate first to the tungsten center, then to the cubane cluster and finally to the ferredoxin.