title: Characterization of the ornithine aminotransferase from Plasmodium falciparum.
abstract: The ornithine aminotransferase from Plasmodium falciparum 3D7 was cloned, functionally expressed, and characterized. The gene exists as a single copy in the malarial genome and is located on chromosomes 6/7/8. The deduced amino acid sequence was found to be 85% identical to a similar sequence discovered in Plasmodium yoelii, 82% identical to a partial sequence from Plasmodium vivax, and 42-53% identical to ornithine aminotransferases from other eukaryotes. The enzyme had a very narrow substrate specificity, and could only catalyze the transamination of alpha-ketoglutarate with ornithine or N-acetylornithine, and of glutamate-5-semialdehyde with glutamate and alanine. The aminooxy analogue of ornithine, canaline, was found to inhibit the ornithine aminotransferase uncompetatively with a Ki of 492+/-98 nM. As the enzyme effectively catalyzed both ornithine catabolism and formation, its potential role in ornithine biosynthesis from glutamine, via glutamate, glutamate-5-phosphate, and glutamate-5-semialdehyde, was examined. Over the course of a 3.5 h incubation, P. falciparum converted 34% of exogenous, radiolabeled glutamine to glutamate and 0.68% to ornithine. This low level of conversion suggests that the parasite may have alternative mechanisms for obtaining ornithine for polyamine biosynthesis.
authors.affiliation: Department of Biochemistry, University of Dundee, DD1 5EH, Dundee, UK.
authors.forename: C
authors.initials: C
authors.lastname: Gafan
authors.forename: J
authors.initials: J
authors.lastname: Wilson
authors.forename: L C
authors.initials: LC
authors.lastname: Berger
authors.forename: B J
authors.initials: BJ
authors.lastname: Berger
mesh_terms: D000595:Amino Acid Sequence; D000613:Aminobutyrates / Q000494:pharmacology; D000818:Animals; D004912:Erythrocytes / Q000469:parasitology; D006801:Humans; D016778:Malaria, Falciparum / Q000469:parasitology; D008969:Molecular Sequence Data; D009952:Ornithine / Q000378:metabolism; D009953:Ornithine-Oxo-Acid Transaminase / Q000737:chemistry / Q000235:genetics / Q000302:isolation & purification / Q000378:metabolism*; D010963:Plasmodium falciparum / Q000201:enzymology* / Q000235:genetics
chemical_list: D000613:Aminobutyrates; C001926:canaline; D009952:Ornithine; D009953:Ornithine-Oxo-Acid Transaminase