title: L-lactate metabolism in potato tuber mitochondria.
abstract: 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 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. The addition of L-lactate to potato tuber mitochondria caused: (a) a minor reduction of intramitochondrial 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 mitochondria possess a non-energy-competent L-lactate/pyruvate shuttle. We maintain, therefore, that mitochondrial metabolism of L-lactate plays a previously unsuspected role in the response of potato to hypoxic stress.
authors.affiliation: Dipartimento di Scienze per la Salute, Università del Molise, Via De Sanctis, 86100 Campobasso, Italy.
authors.forename: Gianluca
authors.initials: G
authors.lastname: Paventi
authors.forename: Roberto
authors.initials: R
authors.lastname: Pizzuto
authors.forename: Gabriella
authors.initials: G
authors.lastname: Chieppa
authors.forename: Salvatore
authors.initials: S
authors.lastname: Passarella
mesh_terms: D005470:Fluorometry; D007770:L-Lactate Dehydrogenase / Q000378:metabolism; D007773:Lactates / Q000378:metabolism*; D008928:Mitochondria / Q000201:enzymology / Q000378:metabolism*; D010100:Oxygen / Q000378:metabolism; D018517:Plant Roots / Q000378:metabolism*; D011198:Solanum tuberosum / Q000378:metabolism*
chemical_list: D007773:Lactates; D007770:L-Lactate Dehydrogenase; D010100:Oxygen