title: The Contribution of Nicotinamide Nucleotide Transhydrogenase to Peroxide Detoxification Is Dependent on the Respiratory State and Counterbalanced by Other Sources of NADPH in Liver Mitochondria.
abstract: The forward reaction of nicotinamide nucleotide transhydrogenase (NNT) reduces NADP(+) at the expense of NADH oxidation and H(+) movement down the electrochemical potential across the inner mitochondrial membrane, establishing an NADPH/NADP(+) ratio severalfold higher than the NADH/NAD(+) ratio in the matrix. In turn, NADPH drives processes, such as peroxide detoxification and reductive biosynthesis. In this study, we generated a congenic mouse model carrying a mutated Nnt(C57BL/6J) allele from the C57BL/6J substrain. Suspensions of isolated mitochondria from Nnt(+/+), Nnt(+/-), and Nnt(-/-) mouse liver were biochemically evaluated and challenged with exogenous peroxide under different respiratory states. The respiratory substrates were also varied, and the participation of concurrent NADPH sources (i.e. isocitrate dehydrogenase-2, malic enzymes, and glutamate dehydrogenase) was assessed. The principal findings include the following: Nnt(+/-) and Nnt(-/-) exhibit ∼50% and absent NNT activity, respectively, but the activities of concurrent NADPH sources are unchanged. The lack of NNT activity in Nnt(-/-) mice impairs peroxide metabolism in intact mitochondria. The contribution of NNT to peroxide metabolism is decreased during ADP phosphorylation compared with the non-phosphorylating state; however, it is accompanied by increased contributions of concurrent NADPH sources, especially glutamate dehydrogenase. NNT makes a major contribution to peroxide metabolism during the blockage of mitochondrial electron transport. Interestingly, peroxide metabolism in the Nnt(+/-) mitochondria matched that in the Nnt(+/+) mitochondria. Overall, this study demonstrates that the respiratory state and/or substrates that sustain energy metabolism markedly influence the relative contribution of NNT (i.e. varies between nearly 0 and 100%) to NADPH-dependent mitochondrial peroxide metabolism.
authors.affiliation: From the Department of Clinical Pathology, Faculty of Medical Sciences, and.
authors.forename: Juliana Aparecida
authors.initials: JA
authors.lastname: Ronchi
authors.affiliation: From the Department of Clinical Pathology, Faculty of Medical Sciences, and.
authors.forename: Annelise
authors.initials: A
authors.lastname: Francisco
authors.affiliation: Multidisciplinary Center for Biological Investigation on Laboratory Animals Science, University of Campinas, Campinas SP 13083-877, Brazil.
authors.forename: Luiz Augusto Correa
authors.initials: LA
authors.lastname: Passos
authors.affiliation: From the Department of Clinical Pathology, Faculty of Medical Sciences, and figueirat@yahoo.com.br.
authors.forename: Tiago Rezende
authors.initials: TR
authors.lastname: Figueira
authors.affiliation: From the Department of Clinical Pathology, Faculty of Medical Sciences, and roger@fcm.unicamp.br.
authors.forename: Roger Frigério
authors.initials: RF
authors.lastname: Castilho
mesh_terms: D000818:Animals; D004734:Energy Metabolism / Q000502:physiology*; D051379:Mice; D008817:Mice, Mutant Strains; D008930:Mitochondria, Liver / Q000201:enzymology* / Q000235:genetics; D024101:Mitochondrial Proteins / Q000235:genetics / Q000378:metabolism; D009249:NADP / Q000235:genetics / Q000378:metabolism*; D061087:NADP Transhydrogenase, AB-Specific / Q000235:genetics / Q000378:metabolism*; D010101:Oxygen Consumption / Q000502:physiology*; D010545:Peroxides / Q000378:metabolism*
chemical_list: D024101:Mitochondrial Proteins; D010545:Peroxides; D009249:NADP; D061087:NADP Transhydrogenase, AB-Specific; C556048:Nnt protein, mouse
keywords: NADPH; c57bl/6j; hydrogen peroxide; mitochondria; oxidation-reduction (redox); peroxidase; respiratory chain; transhydrogenase; tricarboxylic acid cycle (TCA cycle) (Krebs cycle)