Differential shifts for the backbone nuclei in the two oxidation states of Chromatium vinosum HiPIP are observed. The sizable differential shifts close to the [Fe4S4](n+) cluster are accounted for by the different paramagnetic effects. Residual effects, largest for peptide nitro-ens and not due to known paramagnetic effects, are present at large distances. They arise from the charge difference between the two redox forms of the protein through either long-range conformational changes, polarization effects, or both.