PROSITE documentation PDOC00554
Respiratory-chain NADH dehydrogenase 75 Kd subunit signatures


Respiratory-chain NADH dehydrogenase (EC [1,2] (also known as complex I or NADH-ubiquinone oxidoreductase) is an oligomeric enzymatic complex located in the inner mitochondrial membrane which also seems to exist in the chloroplast and in cyanobacteria (as a NADH-plastoquinone oxidoreductase). Among the 25 to 30 polypeptide subunits of this bioenergetic enzyme complex there is one with a molecular weight of 75 Kd (in mammals), which is the largest subunit of complex I and is a component of the iron-sulfur (IP) fragment of the enzyme. It seems to bind to two 4Fe-4S clusters (called N-3 and N-4).

The 75 Kd subunit is highly similar to [3,4]:

  • Subunit γ of Alcaligenes eutrophus NAD-reducing hydrogenase (gene hoxU) which also binds two 4Fe-4S cluster.
  • Subunit NQO3 of Paracoccus denitrificans NADH-ubiquinone oxidoreductase.
  • Subunit G of Escherichia coli NADH-ubiquinone oxidoreductase (gene nuoG).

The 75 Kd subunit and the bacterial hydrogenase γ subunit contains three conserved clusters of cysteine residues which are most probably involved in the binding of the iron-sulfur clusters. We have developed signature patterns for these three regions.

Last update:

December 2004 / Pattern and text revised.


Technical section

PROSITE methods (with tools and information) covered by this documentation:

COMPLEX1_75K_1, PS00641; Respiratory-chain NADH dehydrogenase 75 Kd subunit signature 1  (PATTERN)

COMPLEX1_75K_2, PS00642; Respiratory-chain NADH dehydrogenase 75 Kd subunit signature 2  (PATTERN)

COMPLEX1_75K_3, PS00643; Respiratory-chain NADH dehydrogenase 75 Kd subunit signature 3  (PATTERN)


1AuthorsRagan C.I.
SourceCurr. Top. Bioenerg. 15:1-36(1987).

2AuthorsWeiss H. Friedrich T. Hofhaus G. Preis D.
TitleThe respiratory-chain NADH dehydrogenase (complex I) of mitochondria.
SourceEur. J. Biochem. 197:563-576(1991).
PubMed ID2029890

3AuthorsFearnley I.M. Walker J.E.
TitleConservation of sequences of subunits of mitochondrial complex I and their relationships with other proteins.
SourceBiochim. Biophys. Acta 1140:105-134(1992).
PubMed ID1445936

4AuthorsWeidner U. Geier S. Ptock A. Friedrich T. Leif H. Weiss H.
TitleThe gene locus of the proton-translocating NADH: ubiquinone oxidoreductase in Escherichia coli. Organization of the 14 genes and relationship between the derived proteins and subunits of mitochondrial complex I.
SourceJ. Mol. Biol. 233:109-122(1993).
PubMed ID7690854

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