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We investigated the metabolism ofl-lactate in mitochondria isolated from potato tubers grown and saved after harvest in the absence of any chemical agents. Immunologic analysis by western blot using goat polyclonal anti-lactate dehydrogenase showed the existence of a mitochondrial lactate dehydrogenase, the activity of which could be measured photometrically only in mitochondria solubilized with Triton X-100. | ỊFEBS Journal L-Lactate metabolism in potato tuber mitochondria Gianluca Paventi Roberto Pizzuto Gabriella Chieppa and Salvatore Passarella Dipartimento di Scienze per la Salute Universita delMolise Campobasso Italy Keywords L-lactate L-lactate dehydrogenase mitochondrial transport plant mitochondria shuttle Correspondence S. Passarella Dipartimento di Scienze per la Salute University delMolise Via De Sanctis 86100 Campobasso Italy Fax 39 0 874 404778 Tel 39 0 874 404868 E-mail passarel@unimol.it Received 2 August 2006 revised 20 December 2006 accepted 10 January 2007 doi 10.1111 j.1742-4658.2007.05687.x We investigated the metabolism of L-lactate in mitochondria isolated from potato tubers grown and saved after harvest in the absence of any chemical agents. Immunologic analysis by western blot using goat polyclonal antilactate dehydrogenase showed the existence of a mitochondrial lactate dehydrogenase the activity of which could be measured photometrically only in mitochondria solubilized with Triton X-100. The addition of L-lac-tate to potato tuber mitochondria caused a a minor reduction of intra-mitochondrial pyridine nucleotides whose measured rate of change increased in the presence of the inhibitor of the alternative oxidase salicyl hydroxamic acid b oxygen consumption not stimulated by ADP but inhibited by salicyl hydroxamic acid and c activation of the alternative oxidase as polarographically monitored in a manner prevented by oxamate an L-lactate dehydrogenase inhibitor. Potato tuber mitochondria were shown to swell in isosmotic solutions of ammonium L-lactate in a stereospecific manner thus showing that L-lactate enters mitochondria by a proton-compensated process. Externally added L-lactate caused the appearance of pyruvate outside mitochondria thus contributing to the oxidation of extramitochondrial NADH. The rate of pyruvate efflux showed a sigmoidal dependence on L-lactate concentration and was inhibited by phenylsuccinate. Hence potato tuber .
