STRUCTURE-FUNCTION STUDIES OF IRON-SULFUR CLUSTERS AND SEMIQUINONES IN THE NADH-Q OXIDOREDUCTASE SEGMENT OF THE RESPIRATORY-CHAIN

Our recent experimental data on iron-sulfur clusters and semiquinones in the complex I segment of the respiratory chain is presented, focusi ng on the Paracoccus (P.) denitrificans and bovine heart studies. The iron-sulfur cluster N2 has attracted the attention of investigators in the research field of complex I, since the mid-point redox potential of this cluster is the highest among all clusters in complex I, and is pH dependent (60 mV/pH). It is known that this cluster is located eit her in the NQO6 (NuoB in E. coli/PSST in bovine heart nomenclature) or in the NQO9 (NuoI/TYKY) subunit in the amphipathic domain of complex I. Our preliminary data indicate that the cluster N2 is located in the NuoB rather than the long-advocated NuoI subunit, and may have a uniq ue Ligand structure. We previously reported spin-spin interactions bet ween cluster N2 and two distinct species of semiquinone (designated SQ (Nf) and SQ(Ns)) associated with complex I. A parallel intensity chang e was observed between the SQ(Nf) (g = 2.00) signal and the N2 split g (parallel to) signal, further supporting our proposed interaction betw een SQ(Nf) and N2 spins. (C) 1998 Elsevier Science BN.