Complex I of Rhodobacter capsulatus and its role in reverted electron transport.
The activities of NAD+-photoreduction and NADH/decyl-ubiquinone reductase in membrane preparations of Rhodobacter capsulatus changed to the same extent under different conditions. These results indicated that NADH:ubiquinone oxidoreductase (complex I) catalyzes the electron transport in the downhill direction (respiratory chain) and in the uphill direction (reverted electron flow). This conclusion was confirmed by the characterization of a complex-I-deficient mutant of R. capsulatus. The mutant was not able to reduce NAD+ in the light. Since this mutant was not able to grow photoautotrophically, we concluded that complex I is the enzyme that catalyzes the reverted electron flow to NAD+ to provide reduction equivalents for CO2 fixation. Complex I is not essential for the reverted electron flow to nitrogenase since the mutant grew under nitrogen-fixing conditions. As shown by immunological means, NuoE, a subunit of complex I from R. capsulatus having an extended C-terminus, was modified depending on the nitrogen source present in the growth medium. When the organism used N2 instead of NH4+, a smaller NuoE polypeptide was synthesized. The complex-I-deficient mutant was not able to modify NuoE. The function of the modification is discussed.
Herter
S M
SM
Institut für Biologie 2, Mikrobiologie, Albert-Ludwigs-Universität Freiburg, Schänzlestrasse 1, D-79104 Freiburg, Germany.
Kortlüke
C M
CM
Drews
G
G
D004579:Electron Transport; D005810:Multigene Family; D009154:Mutation; D009243:NAD / Q000378:metabolism; D016660:NAD(P)H Dehydrogenase (Quinone) / Q000378:metabolism*; D016354:Rhodobacter capsulatus / Q000235:genetics / Q000378:metabolism*
D009243:NAD; D016660:NAD(P)H Dehydrogenase (Quinone)