Structure and evolution of vertebrate aldehyde oxidases: from gene duplication to gene suppression

Aldehyde oxidases (AOXs) and xanthine dehydrogenases (XDHs) belong to the family of molybdo-flavoenzymes. Although AOXs are not identifiable in fungi, these enzymes are represented in certain protists and the majority of plants and vertebrates. The physiological functions and substrates of AOXs are unknown. Nevertheless, AOXs are major drug metabolizing enzymes, oxidizing a wide range of aromatic aldehydes and heterocyclic compounds of medical/toxicological importance. Using genome sequencing data, we predict the structures of AOX genes and pseudogenes, reconstructing their evolution. Fishes are the most primitive organisms with an AOX gene (AOXα), originating from the duplication of an ancestral XDH. Further evolution of fishes resulted in the duplication of AOXα into AOXβ and successive pseudogenization of AOXα. AOXβ is maintained in amphibians and it is the likely precursors of reptilian, avian, and mammalian AOX1. Amphibian AOXγ is a duplication of AOXβ and the likely ancestor of reptilian and avian AOX2, which, in turn, gave rise to mammalian AOX3L1. Subsequent gene duplications generated the two mammalian genes, AOX3 and AOX4. The evolution of mammalian AOX genes is dominated by pseudogenization and deletion events. Our analysis is relevant from a structural point of view, as it provides information on the residues characterizing the three domains of each mammalian AOX isoenzyme. We cloned the cDNAs encoding the AOX proteins of guinea pig and cynomolgus monkeys, two unique species as to the evolution of this enzyme family. We identify chimeric RNAs from the human AOX3 and AOX3L1 pseudogenes with potential to encode a novel microRNA.     

Medium- and short-chain dehydrogenase/reductase gene and protein families

Alcohol dehydrogenase 3 (ADH3) is highly conserved, ubiquitously expressed in mammals and involved in essential cellular pathways. A large active site pocket entails special substrate specificities: shortchain alcohols are poor substrates, while medium-chain alcohols and particularly the glutathione adducts S-hydroxymethylglutathione (HMGSH) and S-nitrosoglutathione (GSNO) are efficiently converted under concomitant use of NAD⁺/NADH. By oxidation of HMGSH, the spontaneous glutathione adduct of formaldehyde, ADH3 is implicated in the detoxification of formaldehyde. Through the GSNO reductase activity, ADH3 can affect the transnitrosation equilibrium between GSNO and S-nitrosated proteins, arguing for an important role in NO homeostasis. Recent findings suggest that ADH3-mediated GSNO reduction and subsequent product formation responds to redox states in terms of NADH availability and glutathione levels. Finally, a dual function of ADH3 is discussed in view of its potential implications for asthma.     

Medium- and short-chain dehydrogenase/reductase gene and protein families

In this report we describe the main features of the initially determined alcohol dehydrogenase, that of horse liver, relate this to the human enzyme structures and review recent structural studies on mutants and new complexes of the enzymes. We further review the structure of a bacterial alcohol dehydrogenase to arrive at a coherent picture of medium-chain dehydrogenase/reductase alcohol dehydrogenases in general.     

Medium- and short-chain dehydrogenase/reductase gene and protein families

The MDR superfamily with ~350-residue subunits contains the classical liver alcohol dehydrogenase (ADH), quinone reductase, leukotriene B4 dehydrogenase and many more forms. ADH is a dimeric zinc metalloprotein and occurs as five different classes in humans, resulting from gene duplications during vertebrate evolution, the first one traced to ~500 MYA (million years ago) from an ancestral formaldehyde dehydrogenase line. Like many duplications at that time, it correlates with enzymogenesis of new activities, contributing to conditions for emergence of vertebrate land life from osseous fish. The speed of changes correlates with function, as do differential evolutionary patterns in separate segments. Subsequent recognitions now define at least 40 human MDR members in the Uniprot database (corresponding to 25 genes when excluding close homologues), and in all species at least 10888 entries. Overall, variability is large, but like for many dehydrogenases, subdivided into constant and variable forms, corresponding to household and emerging enzyme activities, respectively. This review covers basic facts and describes eight large MDR families and nine smaller families. Combined, they have specific substrates in metabolic pathways, some with wide substrate specificity, and several with little known functions.     

Significant differential gene duplication without ancestral tetraploidy in a genus of mexican fish

Summary A comparison of the protein products of 20–25 structural gene loci among the known species of the goodeid fish genusSkiffia suggests that at least 4 loci (16–20%) have undergone species-specific duplications (or, in 1 case, apparent loss) during the evolution of the genus. The species are clearly diploids, and the data therefore indicate that even a large proportion of differentially duplicated loci within a group of related fish species is not critical evidence of common tetraploid ancestry. Differential duplication of structural gene loci may be an important component of the genetic differences that separate congeneric conventional diploid species.Supported by NSF grants DEB76-20958 (BJT), DEB77-03257 (EMR) and DEB77-17315 (RRM).     

Medium- and short-chain dehydrogenase/reductase gene and protein families

Zinc plays an important role in the structure and function of many enzymes, including alcohol dehydrogenases (ADHs) of the MDR type (mediumchain dehydrogenases/reductases). Active site zinc participates in catalytic events, and structural site zinc maintains structural stability. MDR-types of ADHs have both of these zinc sites but with some variation in ligands and spacing. The catalytic zinc sites involve three residues with different spacings from two separate protein segments, while the structural zinc sites involve four residues and cover a local segment of the protein chain (Cys97-Cys111 in horse liver class I ADH). This review summarizes properties of both ADH zinc sites, and relates them to zinc sites of proteins in general. In addition, it highlights a separate study of zinc binding peptide variants of the horse liver ADH structural zinc site. The results show that zinc coordination of the free peptide differs markedly from that of the enzyme (one His / three Cys versus four Cys), suggesting that the protein zinc site is in an energetically strained conformation relative to that of the peptide. This finding is a characteristic of an entatic state, implying a functional nature for this zinc site.     

Medium- and short-chain dehydrogenase/reductase gene and protein families

The structure-function relationships of alcohol dehydrogenases from the large family of short-chain dehydrogenase/reductase (SDR) enzymes are described. It seems that while mammals evolved with a medium-chain alcohol dehydrogenase family (MDR), fruit flies utilized an ancestral SDR enzyme. They have modified its function into an efficient alcohol dehydrogenase to aid them in colonizing the emerging ecological niches that appeared around 65 million years ago. To the scientific community, Drosophila has now served as a model organism for quite some time, and Drosophila alcohol dehydrogenase is one of the best-studied members of the SDR family. The availability of a number of high-resolution structures, accurate and thorough kinetic work, and careful theoretical calculations have enabled an understanding of the structure-function relationships of this metal-free alcohol dehydrogenase. In addition, these studies have given rise to various hypotheses about the mechanism of action of this enzyme and contribute to the detailed knowledge of the large superfamily of SDR enzymes.     

Quantitative distribution of glucose-6-phosphate dehydrogenase and isocitric dehydrogenase in the human nephron

Zusammenfassung In den einzelnen Abschnitten des menschlichen Nephrons und in Nierenhomogenaten wurden quantitativ die Glucose-6-phosphat-dehydrogenase-und die Isozitronens?uredehydrogenase-Aktivit?t gemessen.

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This investigation was made possible by a grant from the Swiss National Foundation for the Development of Scientific Research. The technical assistance of MissD. Keller is gratefully acknowledged.     

Vitamin requirements of decotylised pea seedlings cultivated in the dark

Zusammenfassung Abgeschnittene Erbsenwurzeln wachsen, wie schon frühere Untersuchungen gezeigt haben, unbegrenzt in einer Nährlösung mit Thiamin (Vitamin B₁) und Niacin als die einzigen zugesetzten Vitamine. Das konnte auch mit der in dieser Arbeit verwendeten Erbsenrasse bestätigt werden. Dekotylisierte Erbsenkeimlinge, die unter denselben Bedingungen in Dunkelheit kultiviert wurden, brauchten aber Thiamin undPyridoxin (Vitamin B₆). Ein Bedürfnis von Niacin zeigte sich dagegen während der angewandten Versuchszeit bei diesen Keimlingen nicht.     

Succinic dehydrogenase and isocitric dehydrogenase activities in vitamin E-sufficient and-deficient fetal rats

Zusammenfassung Die vergleichende Untersuchung der Aktivität der Bernsteinsäure- und Isozitronensäuredehydrogenase bei 15–21 Tage alten Rattenföten mit Vitamin-E-Mangel und normalem Gehalt ergab keine bedeutenden Unterschiede zwischen den verschiedenen Organen. Die Gegenwart dieser Enzyme in Osteoblasten, Osteoclasten und Osteocyten ist auffallend.     

Lactate dehydrogenase and glutamate dehydrogenase activities in the circumventricular organs of rat brain following neonatal monosodium glutamate

Glutamate (glu) an excitatory neurotransmitter amino acid, is present in high concentrations in the mammalian central nervous system and is the most abundant amino acid in our daily diet. In the present study the activities of lactate dehydrogenase (LDH) and glutamate dehydrogenase (GDH) were evaluated in the circumventricular organs (CVO) of the brain in 25-day-old rats following MSG administration at a dose of 4 mg/g b.wt during the first ten days of life. The results show the LDH activity increased to 265% of that in the control (p<0.001), whereas GDH activity was significantly decreased (p<0.05), The great elevation in LDH, a cytoplasmic marker enzyme, is apparently due to cytoskeletal changes brought about as a consequence of glu toxicity, whereas lowered GDH activity indicates altered glu homostasis in the blood-brain-barrier deficient areas following neonatal exposure to glu.     

Resistance in some wild and cultivated grasses to the phytotoxicity of a systemic fungicide

Zusammenfassung Auf den Blättern einiger Gräser (Aegilops, Triticum, Secale, Hordeum undAvena) wurde der Grad der durch das systemische Fungizid Calixin verursachten Chlorosis näher untersucht.     

Effects of ethidium bromide in diploid and duplication strains of Aspergillus nidulans

Summary Unstable duplication and diploid strains of Aspergillus nidulans were treated with ethidium bromide, and it was shown that this drug reduces the number of sectors produced by such strains. The mechanisms which could be responsible for the partial stabilization of the strains are discussed and it is suggested that a similar mechanism is responsible for the production of sectors in both strains. It is also suggested that ethidium bromide could be useful for the reduction of instability of industrial strains.Acknowledgment. The authors are thankful to the National Council for the Development of Science and Technology (CNPq) for financial assistance.     

Variation in the lactase dehydrogenase activity of the esophagus

Quantitative assay and electrophoretic study of lactate dehydrogenase (LDH) from various tissues of the opossum esophagus were performed. On the basis of expression of the LDH isozymes, we concluded that the smooth muscle of the body of the esophagus carry on more anaerobic glycolysis than the striated muscle. The smooth muscle of the gastroesophageal junction carry on both anaerobic as well aerobic glycolysis.