Die Exilanten und die heutige amerikanische Universität

Schwarz, Egon

doi:10.1007/978-3-476-03563-9_13

Cited by 2 publications

(5 citation statements)

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“…Again, the current recordings showed direct transitions between the two conductance states (details not shown), indicating that the smaller conductance may be a subconductant level. The rather low-unit conductance obtained for the channel in Figure 2b is almost identical to that obtained for the reconstituted 2-oxoglutarate/malate translocator in solutions with identical ionic strengths (Schwarz, 1994). We therefore conclude that the conductances of the anion channel shown in Figure 2b are carried by the 2-oxoglutarate/malate translocator, while the higher conductance observed in the experiment shown in Figure 2a can be attributed to a different channel.…”

Section: Resultssupporting

confidence: 74%

“…As mentioned above, this is hampered by the presence of metabolite translocators of the chloroplast inner envelope membrane (triose phosphate/phosphate translocator and 2-oxoglutarate/malate translocator) that also reveal anion channel activities (Schwarz et al, 1994;Schwarz, 1994). The conductance of the fully open triose phosphate/phosphate translocator channel was A == 140 pS in 100 mM KC1, and three additional sublevels were observed (Schwarz et al, 1994).…”

Section: Resultsmentioning

confidence: 99%

“…Besides these high-conductance channels, we detected lowconductance channels, mainly permeable to chloride. However, since we previously observed anion channel activities associated with the purified triose phosphate/phosphate translocator and the purified 2-oxoglutarate/malate translocator from the chloroplast inner envelope membrane (Schwarz et al, 1994;Schwarz, 1994), it is not possible to assign this activity unambiguously to a specific anion channel protein.…”

Section: Discussionmentioning

confidence: 95%

“…The conductance of the fully open triose phosphate/phosphate translocator channel was A == 140 pS in 100 mM KC1, and three additional sublevels were observed (Schwarz et al, 1994). The 2-oxoglutarate/malate translocator revealed a rather small main conductance of As 14 pS in symmetrical 100 mM KC1 and was inhibited by the chloride channel inhibitor 5-nitro-2,3-bis[(3-phenylpropyl)amino]benzoate (NPBB) (Schwarz, 1994). In order to obtain a high resolution of anion-selective currents mediated by chloroplast envelope membrane proteins, we employed the patch-clamp technique on giant liposomes containing chloroplast envelope membrane proteins (see Materials and Methods).…”

Section: Resultsmentioning

confidence: 99%

“…In addition to these ion channels, the triose phosphate/phosphate translocator and the 2-oxoglutarate/malate translocator, both being antiport transport systems of the chloroplast inner envelope membrane (Fliigge & Heldt, 1991;Menzlaff & Fliigge, 1993), have been shown to function also as ion channels. The ion channel activities of these antiporters, however, can only be observed if the concentrations of the physiological substrates are low compared to those of monovalent ions (Schwarz et al, 1994;Schwarz, 1994). Similar to the inner mitochondrial membrane, it is conceivable that the chloroplast inner envelope contains, in addition, a protein-containing channel that is part of the chloroplast protein import machinery (Pfanner et al, 1994;Wienhues & Neupert, 1992;Fliigge, 1990;Kessler et al, 1994).…”

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confidence: 99%

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Ion Channels in the Chloroplast Envelope Membrane

Heiber

Steinkamp²,

Hinnah³

et al. 1995

Biochemistry

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Isolated chloroplast envelope membranes were fused with azolectin liposomes. Ion transport across the membrane of these liposomes was investigated by the patch-clamp technique and in planar bilayers. Our results show that the chloroplast envelope contains voltage-dependent anion- and cation-selective channels as well as anion- and cation-selective pores with high conductances. At least one of the high-conductance pores could be located in the chloroplast outer envelope membrane. The low-conductance chloride channel and the potassium channel showed complex gating behavior with subconductant states. Potassium channel gating was affected by monovalent and divalent cations as well as by millimolar concentrations of ATP. Low concentrations of Cs+ induced a flickering block. Voltage dependence of the open probability reveals that macroscopic currents of potassium channels are rectified with preferential potassium uptake into the chloroplast. Flux measurements and determinations of the stroma pH of intact chloroplasts confirm the presence of a potassium channel that is regulated by divalent cations (Mg2+) and by ATP. The fully open potassium channel revealed a conductance of lambda approximately equal to 100 pS in asymmetric KCl (250/20 mM KCl), and the fully open chloride channel revealed a conductance of lambda approximately equal to 60 ps in 100 mM Tris/HCl. One high-conductance channel, mainly active at holding potentials > 60 mV, was slightly selective for glutamate anions (PK+/PGlu- approximately equal to 2) and revealed fast voltage-dependent gating. This high-conductance channel had a conductance of lambda approximately equal to 540 pS (in 250/20 mM potassium glutamate) and was closed most of the time. A second type of high-conductance channel, mainly open and active at holding potentials below 30 mV, was slightly selective for cations (PGlu-/PK+ approximately equal to 2) with a conductance of lambda approximately equal to 1.14 nS (in 250/20 mM potassium glutamate).

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Section: Resultssupporting

confidence: 74%