Isolation and characterisation of subcomplexes of the mitochondrial NADH:ubiquinone oxidoreductase (complex I).
Enzymically active subcomplexes were purified from bovine mitochondrial NADH:ubiquinone oxidoreductase (complex I) by sucrose-gradient centrifugation in the presence of detergents. These subcomplexes, named I lambda, IS, and I lambda S, catalyse ferricyanide and ubiquinone-1 (Q-1) reduction by NADH at similar rates to complex I, but do not catalyse the reduction of decylubiquinone. In addition, the Q-1 reductase activity of all the subcomplexes is insensitive to rotenone. Chemical and EPR analyses of the subcomplexes show that FMN and all the Fe-S clusters of complex I are present, but that the line shape of cluster 2 is modified. The smallest subcomplex, I lambda S, contains only approximately 13 subunits, as compared to approximately 22 in the previously described subcomplex I alpha [Finel, M., Skehel, J. M., Albracht, S. J. P., Fearnley, I. M. & Walker, J. E. (1992) Biochemistry 31, 11425-11434], but it retains the 75-, 51-, 49-, 30-, 24-, 23- (TYKY) and 20-kDa (PSST) subunits, which are suggested to form a functional core that comprises the EPR-detectable Fe-S clusters 1-4, and FMN. The structural and functional implications of such an arrangement are discussed.
Helsinki Bioenergetics Group, Department of Medical Chemistry, University of Helsinki, Finland.
M
M
Finel
A S
AS
Majander
J
J
Tyynelä
A M
AM
De Jong
S P
SP
Albracht
M
M
Wikström
D000595:Amino Acid Sequence; D000818:Animals; D002417:Cattle; D002498:Centrifugation; D004578:Electron Spin Resonance Spectroscopy; D004579:Electron Transport; D042967:Electron Transport Complex I; D004591:Electrophoresis, Polyacrylamide Gel; D005486:Flavin Mononucleotide / Q000032:analysis; D007506:Iron-Sulfur Proteins / Q000032:analysis; D008928:Mitochondria / Q000201:enzymology; D008969:Molecular Sequence Data; D009247:NADH, NADPH Oxidoreductases / Q000737:chemistry / Q000302:isolation & purification*
D007506:Iron-Sulfur Proteins; D005486:Flavin Mononucleotide; D009247:NADH, NADPH Oxidoreductases; D042967:Electron Transport Complex I