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Issue 5, 1994
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Redox reactivity of the binuclear iron active site of porcine purple acid phosphatase (uteroferrin)


Redox interconversions (25 °C) of active FeIIFeIII purple acid phosphatase (PAPr), and the inactive FeIIIFeIII form (PAPo), have been explored at pH 5.0 (close to maximum activity), I= 0.100 M (NaCl). At this pH the PAPo–PAPr, couple has a reduction potential E°′ of 367 mV vs. normal hydrogen electrode. Whereas with [Co(phen)3]3+ as oxidant for PAPr first-order dependencies on both reactants are observed (k= 1.26 M–1 s–1), with [Fe(CN)6]3– saturation kinetics are obtained with association. K= 540 M–1, occurring prior to electron transfer, ket= 1.0 s–1. The latter reaction undergoes competitive inhibition with redox inactive [Cr(CN)6]3–(Kcr= 550 M–1) and [Mo(CN)8]4–(KMo= 1580 M–1) consistent with a positively charged locality on the protein surface influencing reactivity. With [Ru(NH3)6]2+ reduction of PAPo is too fast to monitor, but with the less strongly reducing [Ru(NH3)5(H2O)]2+ a rate law first order in both reactants (k= 2.2 × 105 M–1 s–1) is observed. Reactions of both these reductants with the less strongly oxidising phosphate bound PAPo–PO4 form (183 mV) were also studied. On reduction of PAPr with S2O42– a bleaching of the colour is observed consistent with FeIIFeII formation. After 30 min only 40% of the protein could be restored to one or other of the higher oxidation states, indicating loss of FeII.

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Article type: Paper
DOI: 10.1039/DT9940000683
Citation: J. Chem. Soc., Dalton Trans., 1994,0, 683-687
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    Redox reactivity of the binuclear iron active site of porcine purple acid phosphatase (uteroferrin)

    M. A. S. Aquino and A. G. Sykes, J. Chem. Soc., Dalton Trans., 1994, 0, 683
    DOI: 10.1039/DT9940000683

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