Uncoupling protein-1 is not leaky.
2010 (English)In: Biochimica et Biophysica Acta, ISSN 0006-3002, Vol. 1797, no 6-7, 773-84 p.Article in journal (Refereed) Published
The activity of uncoupling protein-1 (UCP1) is rate-limiting for nonshivering thermogenesis and diet-induced thermogenesis. Characteristically, this activity is inhibited by GDP experimentally and presumably mainly by cytosolic ATP within brown-fat cells. The issue as to whether UCP1 has a residual proton conductance even when fully saturated with GDP/ATP (as has recently been suggested) has not only scientific but also applied interest, since a residual proton conductance would make overexpressed UCP1 weight-reducing even without physiological/pharmacological activation. To examine this question, we have here established optimal conditions for studying the bioenergetics of wild-type and UCP1(-/-) brown-fat mitochondria, analysing UCP1-mediated differences in parallel preparations of brown-fat mitochondria from both genotypes. Comparing different substrates, we find that pyruvate (or palmitoyl-l-carnitine) shows the largest relative coupling by GDP. Comparing albumin concentrations, we find the range 0.1-0.6% optimal; higher concentrations are inhibitory. Comparing basic medium composition, we find 125mM sucrose optimal; an ionic medium (50-100mM KCl) functions for wild-type but is detrimental for UCP1(-/-) mitochondria. Using optimal conditions, we find no evidence for a residual proton conductance (not a higher post-GDP respiration, a lower membrane potential or an altered proton leak at highest common potential) with either pyruvate or glycerol-3-phosphate as substrates, nor by a 3-4-fold alteration of the amount of UCP1. We could demonstrate that certain experimental conditions, due to respiratoty inhibition, could lead to the suggestion that UCP1 possesses a residual proton conductance but find that under optimal conditions our experiments concur with implications from physiological observations that in the presence of inhibitory nucleotides, UCP1 is not leaky.
Place, publisher, year, edition, pages
2010. Vol. 1797, no 6-7, 773-84 p.
IdentifiersURN: urn:nbn:se:su:diva-45245DOI: 10.1016/j.bbabio.2010.04.007PubMedID: 20399195OAI: oai:DiVA.org:su-45245DiVA: diva2:368146