Characterization of a New Thioredoxin System from Entamoeba histolytica

D.G. ARIAS, A.A. IGLESIAS, S.A. GUERRERO

Mar del Plata, Buenos Aires, Argentina

Congreso; XLIII Reunión Anual de SAIB; 2007

SAIB

EN-P16.CHARACTERIZATION OF A NEW THIOREDOXINSYSTEMFROMENTAMOEBAHISTOLYTICAArias DG, Iglesias AA, Guerrero SA.UNL-CONICET, Facultad de Bioquímica y Ciencias Biológicas,3000 Santa Fe. E-mail: darias@fbcb.unl.edu.arThe thioredoxin system, composed by thioredoxin and thioredoxinreductase, serves as a reduction equivalents donor in the reductionof disulfides. , a unicellular parasite, usuallylives and multiplies within the human gut, under reduced oxygenpressure. During tissue invasion, it is exposed to increased amountsof reactive oxygen species, which are highly toxic for the parasite.The metabolic pathways used by this organism to cope with suchenvironmental changes and redox homeostasis are a matter of ourwork. Recently, we characterized in its functionalthioredoxin system ( TRXR/ TRX41). In this work, wepresent the cloning, expression and characterization of a newthioredoxin from ( TRX8). TRX8 wasevaluated in its ability to catalyse theNADPHdependent reductionof cystine (k = 124,7 M s ), GSSG (k = 55.23 M s ), TS (k =118,56 M s ) and insulin (k = 2435.13 M s ). In addition, theTRXR/ TRX8 system was able to work together to P29 (atypical 2CysPrx) in the NADPH dependent reduction ofhydroperoxides. The standard redox potential of TRX8 (-0.282V) was estimated by equilibrium with NADPH/NADP at pH 7.0.This work strongly supports the occurrence in of anew thioredoxin, which was not previously described in theparasite.