title: Purification of three aminotransferases from Hydrogenobacter thermophilus TK-6--novel types of alanine or glycine aminotransferase: enzymes and catalysis.
abstract: Aminotransferases catalyse synthetic and degradative reactions of amino acids, and serve as a key linkage between central carbon and nitrogen metabolism in most organisms. In this study, three aminotransferases (AT1, AT2 and AT3) were purified and characterized from Hydrogenobacter thermophilus, a hydrogen-oxidizing chemolithoautotrophic bacterium, which has been reported to possess unique features in its carbon and nitrogen anabolism. AT1, AT2 and AT3 exhibited glutamate:oxaloacetate aminotransferase, glutamate:pyruvate aminotransferase and alanine:glyoxylate aminotransferase activities, respectively. In addition, both AT1 and AT2 catalysed a glutamate:glyoxylate aminotransferase reaction. Interestingly, phylogenetic analysis showed that AT2 belongs to aminotransferase family IV, whereas known glutamate:pyruvate aminotransferases and glutamate:glyoxylate aminotransferases are members of family Igamma. In contrast, AT3 was classified into family I, distant from eukaryotic alanine:glyoxylate aminotransferases which belong to family IV. Although Thermococcus litoralis alanine:glyoxylate aminotransferase is the sole known example of family I alanine:glyoxylate aminotransferases, it is indicated that this alanine:glyoxylate aminotransferase and AT3 are derived from distinct lineages within family I, because neither high sequence similarity nor putative substrate-binding residues are shared by these two enzymes. To our knowledge, this study is the first report of the primary structure of bacterial glutamate:glyoxylate aminotransferase and alanine:glyoxylate aminotransferase, and demonstrates the presence of novel types of aminotransferase phylogenetically distinct from known eukaryotic and archaeal isozymes.
authors.affiliation: Department of Biotechnology, The University of Tokyo, Tokyo, Japan.
authors.forename: Masafumi
authors.initials: M
authors.lastname: Kameya
authors.forename: Hiroyuki
authors.initials: H
authors.lastname: Arai
authors.forename: Masaharu
authors.initials: M
authors.lastname: Ishii
authors.forename: Yasuo
authors.initials: Y
authors.lastname: Igarashi
mesh_terms: D000410:Alanine Transaminase / Q000235:genetics / Q000302:isolation & purification* / Q000378:metabolism; D000595:Amino Acid Sequence; D002384:Catalysis; D017124:Conserved Sequence; D056890:Eukaryota / Q000201:enzymology*; D051308:Glycine Transaminase / Q000235:genetics / Q000302:isolation & purification* / Q000378:metabolism; D007527:Isoenzymes / Q000235:genetics / Q000302:isolation & purification / Q000378:metabolism; D007700:Kinetics; D008954:Models, Biological; D008969:Molecular Sequence Data; D010802:Phylogeny; D013379:Substrate Specificity / Q000235:genetics; D000637:Transaminases / Q000235:genetics / Q000302:isolation & purification* / Q000378:metabolism
chemical_list: D007527:Isoenzymes; D000637:Transaminases; D000410:Alanine Transaminase; D051308:Glycine Transaminase