Cyanobacteria contain a mitochondrial complex I-homologous NADH-dehydrogenase.

Thylakoid and cytoplasmic membranes of the cyanobacterium Synechocystis sp. PCC 6803 were purified by sucrose gradient centrifugation. Both membranes oxidize NADH in a rotenone-sensitive reaction. Antibodies prepared against psbG/ndhK and ndhJ fusion proteins detect the corresponding polypeptides in both membrane preparations. This demonstrates that a NADH-dehydrogenase, homologous to the mitochondrial NADH-ubiquinone-oxidoreductase (complex I of the respiratory chain) is present in cyanobacteria. The NADH-dehydrogenase can be solubilized with the detergent beta-D-dodecylmaltoside. Sedimentation analysis of the solubilized enzyme on a sucrose gradient indicates that it is a multisubunit protein complex.