H-1-NMR SPECTRA OF OXIDIZED HIGH-POTENTIAL IRON SULFUR PROTEIN (HIPIP) FROM RHODOCYCLUS-GELATINOSUS - A MODEL FOR OXIDIZED HIPIPS

The assignment of the beta-CH2 cysteinyl resonances of the oxidized and reduced high-potential iron protein (HiPIP) from Rhodocyclus gelatinosus (formerly Rhodopseudomonas gelatinosa) has been proposed through H-1 NOE, NOESY, and EXSY measurements. The interest has been focused on the oxidized protein for which the comparison of the isotropic shift values and their temperature dependence with those of Chromatium vinosum and Ectothiorhodospira halophila II HiPIPs is rationalized on the basis of theoretical calculations. Such calculations have been performed by utilizing a magnetic exchange spin Hamiltonian with and without the introduction of a double-exchange parameter. No appreciable difference in the energy level pattern is noticed between the two treatments. All the data point toward a cluster with a mixed-valence pair Fe(III)-Fe(II) and two pure Fe(III) ions. The inequivalence between the two Fe(III) ions distinguishes the three proteins. The low-temperature Mossbauer spectra of C. vinosum are rationalized.