title: The alternative NADH dehydrogenase is present in mitochondria of some animal taxa.
abstract: The distribution of the alternative NADH dehydrogenase (NDH-2) in the living world was explored. The enzyme, although present in representatives of all living kingdoms, does not have a universal distribution. With the exception of ε-proteobacteria, the enzyme was found in all eubacterial groups. In contrast with the known presence of the NDH-2 in Archaea, the alternative oxidase (AOX) is absent in this group. With regard to the Eukarya domain, the NDH-2 was found in representatives of Protista, Fungi, Plantae, and Animalia. In the latter, however, the presence of the enzyme was restricted to some primitive Metazoa (Placozoa and Cnidaria), and two members of the Deuterostomate lineage of the Bilateria (Echinodermata and Urochordata). No evidence for the presence of the NDH-2 was found in any representative of the Protostomate branch of the Bilateria, contrasting with the existence of the AOX in this same group. It is worth mentioning that those animal species containing the NDH-2 also have an AOX. The actual distribution of the NDH-2 in the various living kingdoms is discussed within the framework of the endosymbiotic theory; in addition, a hypothesis is proposed to explain the disappearance of the alternative NDH-2 and AOX from the majority of the animals.
authors.affiliation: Departamento de Bioquímica, Universidad Nacional Autónoma de México, Coyoacán, USA.
authors.forename: Macario Genaro
authors.initials: MG
authors.lastname: Matus-Ortega
authors.forename: Karina Gabriela
authors.initials: KG
authors.lastname: Salmerón-Santiago
authors.forename: Oscar
authors.initials: O
authors.lastname: Flores-Herrera
authors.forename: Guadalupe
authors.initials: G
authors.lastname: Guerra-Sánchez
authors.forename: Federico
authors.initials: F
authors.lastname: Martínez
authors.forename: Juan Luis
authors.initials: JL
authors.lastname: Rendón
authors.forename: Juan Pablo
authors.initials: JP
authors.lastname: Pardo
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D001105:Archaea / Q000201:enzymology; D001419:Bacteria / Q000201:enzymology; D019295:Computational Biology; D019143:Evolution, Molecular; D007527:Isoenzymes / Q000145:classification / Q000235:genetics / Q000378:metabolism*; D008928:Mitochondria / Q000201:enzymology*; D024101:Mitochondrial Proteins / Q000145:classification / Q000235:genetics / Q000378:metabolism; D008969:Molecular Sequence Data; D009245:NADH Dehydrogenase / Q000145:classification / Q000235:genetics / Q000378:metabolism*; D010088:Oxidoreductases / Q000145:classification / Q000235:genetics / Q000378:metabolism; D010802:Phylogeny; D010940:Plant Proteins / Q000145:classification / Q000235:genetics / Q000378:metabolism; D016415:Sequence Alignment; D000099188:Alternative Oxidase
chemical_list: D007527:Isoenzymes; D024101:Mitochondrial Proteins; D009245:NADH Dehydrogenase; D010088:Oxidoreductases; D010940:Plant Proteins; D000099188:Alternative Oxidase