title: Entamoeba histolytica thioredoxin reductase: molecular and functional characterization of its atypical properties.
abstract: BACKGROUND
  Entamoeba histolytica, an intestinal protozoan that is the causative agent of amoebiasis, is exposed to elevated amounts of highly toxic reactive oxygen and nitrogen species during tissue invasion. Thioredoxin reductase catalyzes the reversible transfer of reducing equivalents between NADPH and thioredoxin, a small protein that plays key metabolic functions in maintaining the intracellular redox balance.
  
  
  METHODS
  The present work deals with in vitro steady state kinetic studies aimed to reach a better understanding of the kinetic and structural properties of thioredoxin reductase from E. histolytica (EhTRXR).
  
  
  RESULTS
  Our results support that native EhTRXR is a homodimeric covalent protein that is able to catalyze the NAD(P)H-dependent reduction of amoebic thioredoxins and S-nitrosothiols. In addition, the enzyme exhibited NAD(P)H dependent oxidase activity, which generates hydrogen peroxide from molecular oxygen. The enzyme can reduce compounds like methylene blue, quinones, ferricyanide or nitro-derivatives; all alternative substrates displaying a relative high capacity to inhibit disulfide reductase activity of EhTRXR.
  
  
  CONCLUSIONS
  Interestingly, EhTRXR exhibited kinetic and structural properties that differ from other low molecular weight TRXR. The TRX system could play an important role in the parasite defense against reactive species. The latter should be critical during the extra intestinal phase of the amoebic infection. So far we know, this is the first in depth characterization of EhTRXR activity and functionality.
authors.affiliation: Instituto de Agrobiotecnología del Litoral, Facultad de Bioquímica y Ciencias Biológicas, Santa Fe, Argentina.
authors.forename: Diego G
authors.initials: DG
authors.lastname: Arias
authors.forename: Erika L
authors.initials: EL
authors.lastname: Regner
authors.forename: Alberto A
authors.initials: AA
authors.lastname: Iglesias
authors.forename: Sergio A
authors.initials: SA
authors.lastname: Guerrero
mesh_terms: D004748:Entamoeba histolytica / Q000201:enzymology*; D005182:Flavin-Adenine Dinucleotide / Q000378:metabolism; D006861:Hydrogen Peroxide / Q000378:metabolism*; D007700:Kinetics; D009243:NAD / Q000378:metabolism; D016660:NAD(P)H Dehydrogenase (Quinone) / Q000378:metabolism; D009249:NADP / Q000378:metabolism; D010084:Oxidation-Reduction; D018384:Oxidative Stress; D026403:S-Nitrosothiols / Q000737:chemistry*; D013880:Thioredoxin-Disulfide Reductase / Q000378:metabolism*; D013879:Thioredoxins / Q000378:metabolism*
chemical_list: D026403:S-Nitrosothiols; D009243:NAD; D005182:Flavin-Adenine Dinucleotide; D013879:Thioredoxins; D009249:NADP; D006861:Hydrogen Peroxide; D016660:NAD(P)H Dehydrogenase (Quinone); D013880:Thioredoxin-Disulfide Reductase