X-band ESEEM spectroscopy of 15N substituted native and inhibitor-bound superoxide dismutase. Hyperfine couplings with remote nitrogen of histidine ligands.

The hyperfine couplings of the remote nitrogens of histidine ligands are determined for the first time by an X-band ESEEM spectroscopy study of 15N-substituted superoxide dismutase (SOD). They show a significant difference between two groups of ligands with different orientation relative to the metal ion. The ESEEM spectra of 15N SOD with cyanide as an inhibitor containing 14N and 15N are also discussed. They allow some conclusions to be drawn about structural changes upon inhibitor binding and indicate the necessity of further multifrequency investigations.