title: Hydrogen peroxide metabolism and sensing in human erythrocytes: a validated kinetic model and reappraisal of the role of peroxiredoxin II.
abstract: Hydrogen peroxide (H2O2) metabolism in human erythrocytes has been thoroughly investigated, but unclear points persist. By integrating the available data into a mathematical model that accurately represents the current understanding and comparing computational predictions to observations we sought to (a) identify inconsistencies in present knowledge, (b) propose resolutions, and (c) examine their functional implications. The systematic confrontation of computational predictions with experimental observations of the responses of intact erythrocytes highlighted the following important discrepancy. The high rate constant (10(7)-10(8) M(-1) s(-1)) for H2O2 reduction determined for purified peroxiredoxin II (Prx2) and the high abundance of this protein indicate that under physiological conditions it consumes practically all the H2O2. However, this is inconsistent with extensive evidence that Prx2's contribution to H2O2 elimination is comparable to that of catalase. Models modified such that Prx2's effective peroxidase activity is just 10(5) M(-1) s(-1) agree near quantitatively with extensive experimental observations. This low effective activity is probably due to a strong but readily reversible inhibition of Prx2's peroxidatic activity in intact cells, implying that the main role of Prx2 in human erythrocytes is not to eliminate peroxide substrates. Simulations of the responses to physiological H2O2 stimuli highlight that a design combining abundant Prx2 with a low effective peroxidase activity spares NADPH while improving potential signaling properties of the Prx2/thioredoxin/thioredoxin reductase system.
authors: Center for Neuroscience and Cell Biology, University of Coimbra, 3004-517 Coimbra, Portugal; Institute for Interdisciplinary Research, University of Coimbra, 3030-789 Coimbra, Portugal.
authors: Rui
authors: R
authors: Benfeitas
authors: Center for Neuroscience and Cell Biology, University of Coimbra, 3004-517 Coimbra, Portugal.
authors: Gianluca
authors: G
authors: Selvaggio
authors: Departamento de Química e Bioquímica and Centro de Química e Bioquímica, Faculdade de Ciências, Universidade de Lisboa, Lisboa, Portugal.
authors: Fernando
authors: F
authors: Antunes
authors: Center for Neuroscience and Cell Biology, University of Coimbra, 3004-517 Coimbra, Portugal.
authors: Pedro M B M
authors: PM
authors: Coelho
authors: Center for Neuroscience and Cell Biology, University of Coimbra, 3004-517 Coimbra, Portugal; Coimbra Chemistry Center, University of Coimbra, 3004-535 Coimbra, Portugal. Electronic address: salvador@cnc.uc.pt.
authors: Armindo
authors: A
authors: Salvador
mesh_terms: D002374:Catalase / Q000378:metabolism; D019295:Computational Biology; D004912:Erythrocytes / Q000378:metabolism*; D006801:Humans; D006861:Hydrogen Peroxide / Q000378:metabolism*; D007700:Kinetics; D008954:Models, Biological; D009249:NADP / Q000378:metabolism; D010084:Oxidation-Reduction; D018384:Oxidative Stress; D054464:Peroxiredoxins / Q000502:physiology*; D015398:Signal Transduction
chemical_list: D009249:NADP; D006861:Hydrogen Peroxide; C086065:PRDX2 protein, human; D054464:Peroxiredoxins; D002374:Catalase
keywords: Free radicals; Peroxiredoxin sulfinylation; Quantitative redox biology; Redox signaling; Systems biology; Thioredoxin