High-potential proteins

High-potential protein from Chromatium vinosum (Fe3+/Fe2+) 0.11... 

Hemoglobin, nitrosyl-, 1194 Hemoproteins, 259 High-potential proteins, 238 Horseradish peroxidase, 265 Hydrogenation... 

Fd = ferredoxin. HP = "high-potential" protein, isolated. Nitrogenase. 

The two species represented in equation 29.13 do not actually possess localized Fe(ll) and Fe(III) centres, rather the electrons are delocaUzed over the cluster core. One could envisage further oxidation to species that are formally 3Fe(III) Fe(II) and 4Fe(III). Whereas the latter is never accessed under physiological conditions, 3Fe(III)-Fe(II) is the oxidized form of HIPIP (high-potential protein), i.e. 2Fe(III) 2Fe(II) is the reduced form of HIPIP or the oxidized form of ferredoxin. In contrast to the reduction potentials of ferredoxins, those of HIPIPs are positive, e.g. -1-360 mV for HIPIP isolated from the bacterium Chromatium vinosum. 

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