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NADH: ubiquinone oxidoreductase (complex 1)

The mitochondrial reduced nicotinamide adenine dinucleotide 1,4-dihydroxynicotinamide adenine dinucleotide ubiquinone oxireductase (NADH-CoQ reductase) (complex I) catalyses electron transfer from NADH to ubiquinone Q10 in a process coupled with an active efflux of protons through the mitochondrial inner membrane. Complex I is the least understood of the enzymes of the mitochondrial respiratory chain. This membranous enzyme is made of 43 subunits and contains 1 flavin mononucleotide (FMN) cofactor and 4-6 iron-sulphur clusters. Such a complexity greatly hinders the analysis of the structure and function of the mitochondrial complex I. Both chloroplasts and prokaryotes such as Rhodobacter capsulatus possess a NADH-CoQ reductase similar to the mitochondrial complex I although apparently simpler.

A joint study has been undertaken of the structural features of the mitochondrial, bacterial and chloroplast NADH-CoQ reductase from bovine mitochondria, pea chloroplast and from the bacterium Rhodobacter capsulatus.

Bovine subcomplexes I-alpha and I-lambda have been isolated. The electron paramagnetic resonance (EPR) characteristics of these complexes have been defined. The 75, 23, 51 and 24 kd subunits of the bovine enzyme have been made in bacteria. The radioactive photoaffinity analogue tritium2azido-nicotinamide adenine dinucleotide (NAD) has been synthesized and the complete gene cluster (19 kb) of the Rhodobacter capsulatus enzyme has been sequenced. Bovine heat shock protein (HSP) 10 has been sequenced and antibodies against bovine 75, 51, 24 and 23 were obtained. Fragments of pea chloroplast ndh K and ndh I were sequenced and expressed in bacteria.

Reported by

MRC Laboratory of Molecular Biology
Hills Road
CB2 2QH Cambridge
United Kingdom
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