Phthalate Dioxygenase Reductase PDR

The midpoint redox potentials for flavin reduction in PDR are E ox/sq = nl74mV for the first couple and E sq/red = n274mV for the second couple (Gassner et al., 1995). The potential for the 2Fe-2S center is E p = nl74 mV. Thus, the thermodynamic driving force favors reduction of the 2Fe-2S center, especially by the first electron transfer. The rate of intramolecular electron transfer for the reduced flavin to the oxidized 2Fe-2S center has been estimated at 200sec based on simulation of stopped flow kinetic data (Correll et ah, 1992). 

FIGURE 11. stereo diagram of phthalate dioxygenase reductase. The FMN- and NADPH-binding domains are on the top and the 2Fe-2S binding domain is on the bottom. The FMN and 2Fe-2S prosthetic groups are shown as skeletal models. 

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Similarly, for 2Fe(2-,3-) clusters in protein environments, the redox shift between Anabaena ferredoxin (a single domain protein) and phthalate dioxygenase reductase (PDR, a three-domain protein which is reasonably homologous in the first domain) was reasonably reproduced PDR has a more positive potential by about 0.2 eV and the theoretical shift prediction is close to this, whether by a single cycle Poisson-Boltzmann calculation or with more elaborate SCRF methodology. This redox shift can be traced mainly to one additional strong N—H—S hydrogen bond... 

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