title: Trypanosoma cruzi trypanothione reductase is inactivated by peroxidase-generated phenothiazine cationic radicals.
abstract: Trypanosoma cruzi trypanothione reductase (TR) was irreversibly inhibited by peroxidase/H2O2 /phenothiazine (PTZ) systems. TR inactivation depended on (a) time of incubation with the phenothiazine system; (b) the peroxidase nature and (c) the PTZ structure and concentration. With the most effective systems, TR inactivation kinetics were biphasic, with a relatively fast initial phase during which about 75% of the enzyme activity was lost, followed by a slower phase leading to total enzyme inactivation. GSH prevented TR inactivation by the peroxidase/H2O2/PTZ+* systems. Production of PTZ+* cation radicals by PTZ peroxidation was essential for TR inactivation. Horseradish peroxidase, leukocyte myeloperoxidase (MPO) and the pseudo-peroxidase myoglobin (Mb) were effective catalysts of PTZ+* production. Promazine, thioridazine, chlorpromazine, propionylpromazine prochlorperazine, perphenazine and trimeprazine were effective constituents of the HRP/H2O2 /PTZ system. The presence of substituents at the PTZ nucleus position 2 exerted significant influence on PTZ activity, as shown by the different effects of 2-trifluoromethyl and 2-H or 2-chlorophenothiazines. The PTZ+* cation radicals disproportionation regenerated the non-radical PTZ molecule and produced the PTZ sulfoxide that was inactive on TR. Thiol compounds including GSH interacted with PTZ+* cation radicals transferring an electron from the sulfide anion to the PTZ+*, thus nullifying the PTZ+* biological and chemical activities.
authors.affiliation: Bioenergetics Research Centre, School of Medicine, University of Buenos Aires, Paraguay 2155, 1121-Buenos Aires, Argentina.
authors.forename: J
authors.initials: J
authors.lastname: Gutierrez-Correa
authors.forename: A H
authors.initials: AH
authors.lastname: Fairlamb
authors.forename: A O
authors.initials: AO
authors.lastname: Stoppani
mesh_terms: D000818:Animals; D002414:Cations, Monovalent; D004578:Electron Spin Resonance Spectroscopy; D004791:Enzyme Inhibitors / Q000494:pharmacology*; D005609:Free Radicals; D006735:Horseradish Peroxidase / Q000378:metabolism / Q000494:pharmacology; D006861:Hydrogen Peroxide / Q000378:metabolism / Q000494:pharmacology; D007700:Kinetics; D009211:Myoglobin / Q000378:metabolism / Q000494:pharmacology; D009247:NADH, NADPH Oxidoreductases / Q000187:drug effects*; D009195:Peroxidase / Q000378:metabolism / Q000494:pharmacology; D010640:Phenothiazines / Q000378:metabolism / Q000494:pharmacology; D017382:Reactive Oxygen Species / Q000378:metabolism*; D011994:Recombinant Proteins / Q000037:antagonists & inhibitors; D013329:Structure-Activity Relationship; D013438:Sulfhydryl Compounds / Q000494:pharmacology; D013997:Time Factors; D014349:Trypanosoma cruzi
chemical_list: D002414:Cations, Monovalent; D004791:Enzyme Inhibitors; D005609:Free Radicals; D009211:Myoglobin; D010640:Phenothiazines; D017382:Reactive Oxygen Species; D011994:Recombinant Proteins; D013438:Sulfhydryl Compounds; D006861:Hydrogen Peroxide; D006735:Horseradish Peroxidase; D009195:Peroxidase; D009247:NADH, NADPH Oxidoreductases; C049608:trypanothione reductase