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J. Biol. Chem., Vol. 280, Issue 48, 39882-39889, December 2, 2005

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Transport Activity of MCT1 Expressed in Xenopus Oocytes Is Increased by Interaction with Carbonic Anhydrase^*

Holger M. Becker, Daniela Hirnet, Claudia Fecher-Trost, Dieter Sültemeyer¶, and Joachim W. Deitmer1

From the Abteilungen Allgemeine Zoologie, Proteinfunktion/Proteomics, and ^¶Pflanzenökologie & Systematik, Fachbereich Biologie, Technische Universität Kaiserslautern, P. O. Box 3049, D-67653 Kaiserslautern, Germany

Injection of carbonic anhydrase isoform II (CA) into Xenopus frog oocytes increased the rate of H⁺ flux via the rat monocarboxylate transporter isoform 1 (MCT1) expressed in the oocytes. MCT1 activity was assessed by changes of intracellular H⁺ concentration measured by pH-selective microelectrodes during application of lactate. CA-induced augmentation of the rate of H⁺ flux mediated by MCT1 was not inhibited by ethoxyzolamide (10 µM) and did not depend on the presence of added but was suppressed by injection of an antibody against CA. Deleting the C terminus of the MCT1 greatly reduced its transport rate and removed transport facilitation by CA. Injected CA accelerated the acidification severalfold, which was blocked by ethoxyzolamide and was independent of MCT1 expression. Mass spectrometry confirmed activity of CA as injected into the frog oocytes. With pulldown assays we demonstrated a specific binding of CA to MCT1 that was not attributed to the C terminus of MCT1. Our results suggest that CA enhances MCT1 transport activity, independent of its enzymatic reaction center, presumably by binding to MCT1.

Received for publication, March 21, 2005 , and in revised form, September 13, 2005.

^* This study was supported by the Rheinland-Pfalz-Stiftung Innovation and by Deutsche Forschungsgemeinschaft Grants De 231/16-2, and 16-4, and Graduiertenkolleg 845/1. The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore be hereby marked "advertisement" in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.

¹ To whom correspondence should be addressed: Fachbereich Biologie, Technische Universität Kaiserslautern, P. O. Box 3049, D-67653 Kaiserslautern, Germany. Tel.: 49-631-2052877; Fax: 49-631-2053515. E-mail: deitmer{at}rhrk.uni-kl.de.

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