Mössbauer analysis of the binuclear iron site in purple acid phosphatase from pig allantoic fluid

We present a quantitative analysis of the Mossbauer spectra of the spin-coupled two-iron center in porcine purple acid phosphatase. The active enzyme contains a high-spin Fe(III)-Fe(II) pair with a ground state of effective spin S = 1/2 and g tensor g = (1.56, 1.72, 1.93), while the oxidized, inactive enzyme contains a high-spin Fe(III)-Fe(III) pair with a diamagnetic ground state. Preliminary data for metal-substituted and differentially enriched phosphatase are also presented. The parameters of the iron in the Fe-Zn enzyme are found to be close to the intrinsic parameters deduced from the analysis of the native Fe(III)-Fe(II) enzyme, a result that not only corroborates our model but also indicates little change in the iron environment on substitution of zinc.