H NOE studies of oxidized high potential iron sulfur protein II from Ectothiorhodospira halophila

The ¹H NMR spectra of oxidized HiPIP II from Ectothiorhodospira halophila have been recorded at 600 MHz. Nuclear Overhauser effect measurements have allowed the assignment of the cysteine β-CH₂ resonances. Four β-CH₂ signals are downfield shifted and four upfield shifted. Through a theoretical model and on the ground of Mössbauer data on analogous systems we propose that the upfield signals are those of the cysteines bound to the iron(III) ions and those downfield of the cysteines bound to the mixed valence pair Fe(III)-Fe(II).