Biochem. J. (2006) 397
(25–29) (Printed in Great Britain)
Accelerated Publication
The life-extending gene Indy encodes an exchanger for Krebs-cycle intermediates
Felix KNAUF*†‡, Nilufar MOHEBBI*, Carsten TEICHERT*, Diana HEROLD*, Blanka ROGINA§, Stephen HELFAND§, Maik GOLLASCH*, Friedrich C. LUFT* and Peter S. ARONSON†‡1
*Franz Volhard Clinic at the Max Delbruck Center, HELIOS Kliniken – Berlin, Medical Faculty of the Charité, Humboldt University, D-13125 Berlin, Germany, †Department of Internal Medicine, Yale University School of Medicine, New Haven, CT 06520-8029, U.S.A., ‡Department of Cellular and Molecular Physiology, Yale University School of Medicine, New Haven, CT 06520-8029, U.S.A., and §Department of Genetics and Developmental Biology, School of Medicine, University of Connecticut Health Center, Farmington, CT 06030, U.S.A.
A longevity gene called Indy (for ‘I'm not dead yet’), with similarity to mammalian genes encoding sodium–dicarboxylate cotransporters, was identified in Drosophila melanogaster. Functional studies in Xenopus oocytes showed that INDY mediates the flux of dicarboxylates and citrate across the plasma membrane, but the specific transport mechanism mediated by INDY was not identified. To test whether INDY functions as an anion exchanger, we examined whether substrate efflux is stimulated by transportable substrates added to the external medium. Efflux of [14C]citrate from INDY-expressing oocytes was greatly accelerated by the addition of succinate to the external medium, indicating citrate–succinate exchange. The succinate-stimulated [14C]citrate efflux was sensitive to inhibition by DIDS (4,4´-di-isothiocyano-2,2´-disulphonic stilbene), as demonstrated previously for INDY-mediated succinate uptake. INDY-mediated efflux of [14C]citrate was also stimulated by external citrate and oxaloacetate, indicating citrate–citrate and citrate–oxaloacetate exchange. Similarly, efflux of [14C]succinate from INDY-expressing oocytes was stimulated by external citrate, a-oxoglutarate and fumarate, indicating succinate–citrate, succinate–a-oxoglutarate and succinate–fumarate exchange respectively. Conversely, when INDY-expressing Xenopus oocytes were loaded with succinate and citrate, [14C]succinate uptake was markedly stimulated, confirming succinate–succinate and succinate–citrate exchange. Exchange of internal anion for external citrate was markedly pHo-dependent, consistent with the concept that citrate is co-transported with a proton. Anion exchange was sodium-independent. We conclude that INDY functions as an exchanger of dicarboxylate and tricarboxylate Krebs-cycle intermediates. The effect of decreasing INDY activity, as in the long-lived Indy mutants, may be to alter energy metabolism in a manner that favours lifespan extension.
Key words: aging, anion exchange, citrate, dicarboxylate, Indy, succinate.
Abbreviation used: DIDS, 4,4´-di-isothiocyano-2,2´-disulphonic stilbene.
1To whom correspondence should be addressed (email peter.aronson@yale.edu).
Received 15 March 2006/31 March 2006; accepted 12 April 2006
Published as BJ Immediate Publication 12 April 2006, doi:10.1042/BJ20060409
The Biochemical Society, London ©2006
Editorial Advisory Panel
RSS feeds
Table of contents by email
My BJ toolbox
