title: Demonstration of an intramitochondrial invertase activity and the corresponding sugar transporters of the inner mitochondrial membrane in Jerusalem artichoke (Helianthus tuberosus L.) tubers.
abstract: Genetic evidences indicate that alkaline/neutral invertases are present in plant cell organelles, and they might have a novel physiological function in mitochondria. The present study demonstrates an invertase activity in the mitochondrial matrix of Helianthus tuberosus tubers. The pH optimum, the kinetic parameters and the inhibitor profile of the invertase activity indicated that it belongs to the neutral invertases. In accordance with this topology, transport activities responsible for the mediation of influx/efflux of substrate/products were studied in the inner mitochondrial membrane. The transport of sucrose, glucose and fructose was shown to be bidirectional, saturable and independent of the mitochondrial respiration and membrane potential. Sucrose transport was insensitive to the inhibitors of the proton-sucrose symporters. The different kinetic parameters and inhibitors as well as the absence of cross-inhibition suggest that sucrose, glucose and fructose transport are mediated by separate transporters in the inner mitochondrial membrane. The mitochondrial invertase system composed by an enzyme activity in the matrix and the corresponding sugar transporters might have a role in both osmoregulation and intermediary metabolism.
authors.affiliation: Department of Applied Biotechnology and Food Science, Laboratory of Biochemistry and Molecular Biology, Budapest University of Technology and Economics, Muegyetem rakpart 3, 1111, Budapest, Hungary. szarka@mail.bme.hu
authors.forename: András
authors.initials: A
authors.lastname: Szarka
authors.forename: Nele
authors.initials: N
authors.lastname: Horemans
authors.forename: Salvatore
authors.initials: S
authors.lastname: Passarella
authors.forename: Akos
authors.initials: A
authors.lastname: Tarcsay
authors.forename: Ferenc
authors.initials: F
authors.lastname: Orsi
authors.forename: András
authors.initials: A
authors.lastname: Salgó
authors.forename: Gábor
authors.initials: G
authors.lastname: Bánhegyi
mesh_terms: D001692:Biological Transport; D005632:Fructose / Q000378:metabolism; D005947:Glucose / Q000378:metabolism; D006368:Helianthus / Q000378:metabolism*; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D026901:Membrane Transport Proteins / Q000378:metabolism; D051336:Mitochondrial Membranes / Q000378:metabolism*; D035281:Plant Tubers / Q000378:metabolism*; D013395:Sucrose / Q000378:metabolism; D043324:beta-Fructofuranosidase / Q000378:metabolism*
chemical_list: D026901:Membrane Transport Proteins; D005632:Fructose; D013395:Sucrose; D043324:beta-Fructofuranosidase; D005947:Glucose