An analysis of pseudocontact shifts and their relationship to structural features of the redox states of cytochrome b5

The assignment of proton resonances in both redox states of a heme protein is necessary for the evaluation of pseudocontact shift data. Many new assignments are presented here for cytochrome b5, particularly in the paramagnetic oxidised state, thereby allowing both the calculation of electronic g-tensor values with the magnetic axis orientation and a comparison of observed and calculated pseudocontact shifts utilising a computational procedure. The possible redox linked conformational changes are found to be minimal in contrast with cytochrome c although the procedure additionally highlights aspects of the mobility of certain residues in cytochrome b5. In this respect the residue Gly-42 appears mobile both by this method and by the observation from NMR spectra of a major and minor conformation in this region.