Q-BAND ENDOR SPECTRA OF THE RIESKE PROTEIN FROM RHODOBACTOR-CAPSULATUS UBIQUINOL CYTOCHROME-C OXIDOREDUCTASE SHOW 2 HISTIDINES COORDINATED TO THE [2FE-2S] CLUSTER

Electron nuclear double resonance (ENDOR) experiments were performed on N-14 (natural abundance) and N-15-enriched iron-sulfur Rieske protein in the ubiquinol-cytochrome c2 oxidoreductase from Rhodobacter capsulatus. The experiments proved that two distinct nitrogenous ligands, histidines, are undoubtedly ligated to the Rieske [2Fe-2S] center. The calculations of hyperfine tensors give values similar but not identical to those of the Rieske-type cluster in phthalate dioxygenase of Pseudomonas cepacia and suggest a slightly different geometry of the iron-sulfur cluster in the two proteins.