title: Vitamin C biosynthesis in trypanosomes: a role for the glycosome.
abstract: The capacity to synthesize vitamin C (ascorbate) is widespread in eukaryotes but is absent from humans. The last step in the biosynthetic pathway involves the conversion of an aldonolactone substrate to ascorbate, a reaction catalyzed by members of an FAD-dependent family of oxidoreductases. Here we demonstrate that both the African trypanosome, Trypanosoma brucei, and the American trypanosome, Trypanosoma cruzi, have the capacity to synthesize vitamin C and show that this reaction occurs in a unique single-membrane organelle, the glycosome. The corresponding T. brucei flavoprotein (TbALO) obeys Michaelis-Menten kinetics and can utilize both L-galactono-gamma-lactone and D-arabinono-gamma-lactone as substrate, properties characteristic of plant and fungal enzymes. We could detect no activity toward the mammalian enzyme substrate L-gulono-gamma-lactone. TbALO null mutants (bloodstream form) were found to display a transient growth defect, a trait that was enhanced when they were cultured in medium in which the essential serum component had been pretreated with ascorbate oxidase to deplete vitamin C. It is implicit, therefore, that bloodstream-form trypanosomes also possess a capacity for ascorbate transport.
authors.affiliation: Department of Infectious and Tropical Diseases, London School of Hygiene and Tropical Medicine, London WC1E 7HT, United Kingdom. shane.wilkinson@lshtm.ac.uk
authors.forename: Shane R
authors.initials: SR
authors.lastname: Wilkinson
authors.forename: S Radhika
authors.initials: SR
authors.lastname: Prathalingam
authors.forename: Martin C
authors.initials: MC
authors.lastname: Taylor
authors.forename: David
authors.initials: D
authors.lastname: Horn
authors.forename: John M
authors.initials: JM
authors.lastname: Kelly
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D001204:Ascorbate Oxidase / Q000378:metabolism; D001205:Ascorbic Acid / Q000096:biosynthesis* / Q000737:chemistry / Q000378:metabolism; D001692:Biological Transport; D005420:Flavoproteins / Q000235:genetics / Q000378:metabolism; D017125:Genes, Protozoan / Q000235:genetics; D007700:Kinetics; D007783:Lactones / Q000378:metabolism; D008830:Microbodies / Q000378:metabolism*; D008969:Molecular Sequence Data; D009154:Mutation / Q000235:genetics; D015800:Protozoan Proteins / Q000235:genetics / Q000378:metabolism; D016415:Sequence Alignment; D014346:Trypanosoma brucei brucei / Q000166:cytology* / Q000235:genetics / Q000378:metabolism*; D014349:Trypanosoma cruzi / Q000166:cytology* / Q000235:genetics / Q000378:metabolism*
chemical_list: D005420:Flavoproteins; D007783:Lactones; D015800:Protozoan Proteins; D001204:Ascorbate Oxidase; D001205:Ascorbic Acid