High-potential iron-sulfur proteins HiPIPs

High-potential iron-sulfur proteins (HiPIP) form a family of small (—6-10 kDa) soluble electron transport proteins originally only found in photo synthetic representatives of the proteobacteria (for reviews,... 

This cluster formally contains three iron(III) and one iron(E). It is present in a class of proteins called high potential iron-sulfur proteins (HiPIP). It has also been prepared through oxidation of [(RS)4Fe4S4]2 model compounds [57]. Both in the model compound at low temperatures and in proteins there is electron delocalization on one mixed valence pair [58-62]. Therefore, the polymetallic center is constituted by two iron ions at the oxidation state +2.5 and two iron ions at the oxidation state +3. Hamiltonian (6.20), or a more complicated one [40, 41,43], can be used to describe the electronic structure. Indeed, a delocalization operator is sometimes needed in the Hamiltonian [40,41,43]. Consistently with magnetic Mossbauer data the S M subspin involving the mixed valence pair is 9/2, whereas the S n subspin involving the iron(IH) ions is 4. Mossbauer and EPR data do not exclude % and 3, respectively, for the two pairs [57] in any case, the... 

High-Potential Iron-Sulfur Protein (HiPIP)... 

The most thoroughly investigated high-potential iron-sulfur protein (HiPIP) is that isolated for Chromatium vinosum (a purple photosynthetic bacterium). The reduction potential of the iron-sulfur cluster is 350 mV, and the overall charge on the protein is -3 the Fc4S4 cluster is buried within the 9500-Da protein, ligated to cysteines at positions 43,45,63, and 77 (Fig. 12) (1, 18). Several studies have been made of the oxidation and reduction of HiPIP by inorganic complexes (40, 62, 131, 153). 

The superfamily comprises three classes cytochrome c oxidases (CcOs) , quinol oxidases, and cytochrome cbb3 oxidases CcOs are the only HCOs present in eukaryotes. Enzymes of all classes contain a binuclear heme-Cu catalytic site and all act as proton pumps. The water-soluble electron carrier, ferrocytochrome c, is the physiological electron donor for CcOs and cytochrome cbb3 oxidases. Certain CcOs can also oxidize specific high-potential iron-sulfur proteins (HiPIPs). Quinol oxidases catalyze a 2e/2H+ oxidation of various quinols to quinones as the source of electrons for O2 reduction. 

High potential iron-sulfur protein (HiPIP) is a special type of Fd which has been isolated from some photosynthetic bacteria and detected by ESR spectroscopy in other bacteria. HiPIP also contains a single 4Fe-4S cluster, but it differs from the other Fd in having a positive standard potential of about-h 350 mV (most Fd have standard potentials in the range of the hydrogen electrode, about -420 mV). Furthermore, the HiPIP from Chromatium is paramagnetic in the oxidized state. 

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