title: Alamethicin permeabilizes the plasma membrane and mitochondria but not the tonoplast in tobacco (Nicotiana tabacum L. cv Bright Yellow) suspension cells.
abstract: The ion channel-forming peptide AlaM (alamethicin) is known to permeabilize isolated mitochondria as well as animal cells. When intact tobacco (Nicotiana tabacum L.) Bright Yellow-2 cells were treated with AlaM, the cells became permeable for low-molecular-mass molecules as shown by induced leakage of NAD(P)+. After the addition of cofactors and substrates, activities of cytosolic as well as mitochondrial respiratory enzymes could be directly determined inside the permeabilized cells. However, at an AlaM concentration at which the cytoplasmic enzymes were maximally accessible, the vacuole remained intact, as indicated by an unaffected tonoplast proton gradient. Low-flux permeabilization of plasma membranes and mitochondria at moderate AlaM concentrations was reversible and did not affect cell vigour. Higher AlaM concentrations induced cell death. After the addition of catalase that removes the H2O2 necessary for NADH oxidation by apoplastic peroxidases, mitochondrial oxygen consumption could be measured in permeabilized cells. Inhibitor-sensitive oxidation of the respiratory substrates succinate, malate and NADH was observed after the addition of the appropriate coenzymes (ATP, NAD+). The capacities of different pathways in the respiratory electron-transport chain could thus be determined directly. We conclude that AlaM permeabilization provides a very useful tool for monitoring metabolic pathways or individual enzymes in their native proteinaceous environment with controlled cofactor concentrations. Possible uses and limitations of this method for plant cell research are discussed.
authors.affiliation: Department of Cell and Organism Biology, Biology Building, Lund University, Sölvegatan 35B, SE-223 62 Lund, Sweden.
authors.forename: Sandra
authors.initials: S
authors.lastname: Matic
authors.forename: Daniela A
authors.initials: DA
authors.lastname: Geisler
authors.forename: Ian M
authors.initials: IM
authors.lastname: Møller
authors.forename: Susanne
authors.initials: S
authors.lastname: Widell
authors.forename: Allan G
authors.initials: AG
authors.lastname: Rasmusson
mesh_terms: D000408:Alamethicin / Q000494:pharmacology*; D016923:Cell Death / Q000187:drug effects; D002463:Cell Membrane Permeability / Q000187:drug effects*; D002478:Cells, Cultured; D004305:Dose-Response Relationship, Drug; D007425:Intracellular Membranes / Q000187:drug effects; D007476:Ionophores / Q000494:pharmacology*; D008928:Mitochondria / Q000187:drug effects; D009539:Nicotinic Acids; D009711:Nucleotides; D015388:Organelles / Q000187:drug effects*; D010101:Oxygen Consumption; D010539:Permeability; D014026:Nicotiana / Q000187:drug effects* / Q000378:metabolism / Q000648:ultrastructure
chemical_list: D007476:Ionophores; D009539:Nicotinic Acids; D009711:Nucleotides; D000408:Alamethicin