title: The basal proton conductance of skeletal muscle mitochondria from transgenic mice overexpressing or lacking uncoupling protein-3.
abstract: The ability of native uncoupling protein-3 (UCP3) to uncouple mitochondrial oxidative phosphorylation is controversial. We measured the expression level of UCP3 and the proton conductance of skeletal muscle mitochondria isolated from transgenic mice overexpressing human UCP3 (UCP3-tg) and from UCP3 knockout (UCP3-KO) mice. The concentration of UCP3 in UCP3-tg mitochondria was approximately 3 microg/mg protein, approximately 20-fold higher than the wild type value. UCP3-tg mitochondria had increased nonphosphorylating respiration rates, decreased respiratory control, and approximately 4-fold increased proton conductance compared with the wild type. However, this increased uncoupling in UCP3-tg mitochondria was not caused by native function of UCP3 because it was not proportional to the increase in UCP3 concentration and was neither activated by superoxide nor inhibited by GDP. UCP3 was undetectable in mitochondria from UCP3-KO mice. Nevertheless, UCP3-KO mitochondria had unchanged respiration rates, respiratory control ratios, and proton conductance compared with the wild type under a variety of assay conditions. We conclude that uncoupling in UCP3-tg mice is an artifact of transgenic expression, and that UCP3 does not catalyze the basal proton conductance of skeletal muscle mitochondria in the absence of activators such as superoxide.
authors.affiliation: Medical Research Council Dunn Human Nutrition Unit, Hills Road, Cambridge CB2 2XY, United Kingdom.
authors.forename: Susana
authors.initials: S
authors.lastname: Cadenas
authors.forename: Karim S
authors.initials: KS
authors.lastname: Echtay
authors.forename: James A
authors.initials: JA
authors.lastname: Harper
authors.forename: Mika B
authors.initials: MB
authors.lastname: Jekabsons
authors.forename: Julie A
authors.initials: JA
authors.lastname: Buckingham
authors.forename: Evelyn
authors.initials: E
authors.lastname: Grau
authors.forename: Alejandro
authors.initials: A
authors.lastname: Abuin
authors.forename: Helen
authors.initials: H
authors.lastname: Chapman
authors.forename: John C
authors.initials: JC
authors.lastname: Clapham
authors.forename: Martin D
authors.initials: MD
authors.lastname: Brand
mesh_terms: D000818:Animals; D015153:Blotting, Western; D001835:Body Weight; D002352:Carrier Proteins / Q000096:biosynthesis* / Q000235:genetics*; D006801:Humans; D007473:Ion Channels; D007700:Kinetics; D051379:Mice; D018345:Mice, Knockout; D008822:Mice, Transgenic; D008928:Mitochondria / Q000378:metabolism*; D024101:Mitochondrial Proteins; D018482:Muscle, Skeletal / Q000378:metabolism*; D010100:Oxygen / Q000378:metabolism; D010101:Oxygen Consumption; D010766:Phosphorylation; D011485:Protein Binding; D011522:Protons; D019802:Succinic Acid / Q000378:metabolism; D013481:Superoxides / Q000378:metabolism; D000071247:Uncoupling Protein 3
chemical_list: D002352:Carrier Proteins; D007473:Ion Channels; D024101:Mitochondrial Proteins; D011522:Protons; C000604392:UCP3 protein, human; C000604393:Ucp3 protein, mouse; D000071247:Uncoupling Protein 3; D013481:Superoxides; D019802:Succinic Acid; D010100:Oxygen