THE COMPLEX-I FROM RHODOBACTER-CAPSULATUS

The NADH-ubiquinone oxidoreductase (type I NDH) of Rhodobacter capsula tus is a multisubunit enzyme encoded by the 14 genes of the nuo operon . This bacterial enzyme constitutes a valuable model for the character ization of the mitochondrial Complex I structure and enzymatic mechani sm for the following reasons. (i) The mitochondria-encoded ND subunits are not readily accessible to genetic manipulation. In contrast, the equivalents of the mitochondrial ND1, ND2, ND4, ND4L, ND5 and ND6 gene s can be easily mutated in R. capsulatus by homologous recombination. (ii)As illustrated in the case of ND1 gene, point mutations associated with human cytopathies can be reproduced and studied in this model sy stem. (iii) The R. capsulatus model also allows the recombinant manipu lations of iron-sulfur (Fe-S) subunits and the assignment of Fe-S clus ters as illustrated in the case of the NUOI subunit (the equivalent of the mitochondrial TYKY subunit). (iv) Finally, like mitochondrial Com plex I, the NADH-ubiquinone oxidoreductase of R. capsulatus is highly sensitive to the inhibitor piericidin-A which is considered to bind to or close to the quinone binding site(s) of Complex I. Therefore, isol ation of R. capsulatus mutants resistant to piericidin-A represents a straightforward way to map the inhibitor binding sites and to try and define the location of quinone binding site(s) in the enzyme. These il lustrations that describe the interest in the R. capsulatus NADH-ubiqu inone oxidoreductase model for the general study of Complex I will be critically developed in the present review. (C) 1998 Elsevier Science B.V.