Complete tracking of proton flow in thylakoids - the unit conductance of CFo is greater than 10 fS
نویسندگان
چکیده
We investigated the proton conductance of the channel portion of chloroplast ATP synthase (CFa). Thylakoids were CFi-depleted by EDTA treatment. Proton pumps were stimulated by short flashes of light. Proton flux through CFo was measured spectrophotometrically in three different ways: as proton efflux from the lumen (via neutral red), charge flow across the membrane (via electrochromism) and proton influx into the medium (via phenol red). Hence we completely tracked the protons on their way from the lumen through CF,, into the medium. A first treatment with EDTA removed up to 12% of total CFi without increasing the proton permeability of the membranes. A second treatment removed a further 20% of CFi and increased the proton permeability of membranes by 3 orders of magnitude. The electric potential difference and the pH transients, in both the lumen and medium, decayed with a relaxation time of 7 ms indicating electrically driven proton flow through CFo. If the electric driving force was shunted (e.g. by added gramicidin) both pH transients decayed at 85 ms compared with 2&60 s in control thylakoids. The longer relaxation time under chemical driving force was attributable to larger chemical than electrical capacitance of thylakoids. We calculated a lower limit of the unit conductance of CFO under the assumption that all exposed CFo were proton conducting. The value was 10 fS, corresponding to the passage of 6200 protons/s per CFa (at 100 mV electric driving force) and by orders of magnitude higher than so far reported for any F. channel.
منابع مشابه
Complete Tracking of Proton Flow in Thylakoids
Gerald Schoenknecht, Holger Lill, Siegfried Engelbrecht and Wolfgang Junge Biophysik, Fachbereich Biologie/Chemie Universitaet Osnabrueck, Postfach 4469 D-4500 Osnabrueck, Germany (FRG) We investigated the proton conductance of the channel portion of chloroplast ATP synthase (CFo) in thylakoids which were depleted from the soluble portion of the ATP synthase (CF1) by EDTA treatment. Proton pump...
متن کاملReconstitution of CF , - depleted thylakoid membranes with complete and fragmented chloroplast ATPase The role of the 6 subunit for proton conduction through CFo
Chloroplast ATPase (CF,) was isolated from spinach, pea and maize thylakoids by EDTA extraction followed by anion-exchange chromatography. CF1 was purified and resolved by HPLC into integral CF1, and CF, lacking the 6 & E subunits: CF1(-6) and CFl(-E). Washing Mono-Q-bound CFl with alcohol-containing buffers followed by elution without alcohol produced the p subunit and in separate peaks CF1( 6...
متن کاملA New Maximum Power Point Tracking Method for PEM Fuel Cells Based On Water Cycle Algorithm
Maximum Power Point (MPP) tracker has an important role in the performance of fuel cell (FC) systems improvement. Tow parameters which have effect on the Fuel cell output power are temperature and membrane water. So contents make the MPP change by with variations in each parameter. In this paper, a new maximum power point tracking (MPPT) method for Proton Exchange Membrane (PEM) fuel cell is pr...
متن کاملSimulation of a Box Annealing Unit
In this paper the heating process in a box annealing unit is simulated and the effect of various parameters involved in the process is examined. For this purpose, the full Naiver-Stokes equations along with the standard k- turbulence model are solved in the fluid region using the finite volume approach. In the solid area the conduction heat transfer equation is employed using approporate surfac...
متن کاملComplete tracking of transient proton flow through active chloroplast ATP synthase.
Proton pumping in thylakoid membranes and backflow of protons through the active ATP synthase CF0-CF1 (where CF0 is the proton channel and CF1 is the catalytic portion) were investigated by flash spectrophotometry. A steady pH difference across the membrane was generated by continuous measuring light, supplemented by voltage transients that were generated by flashing light. In the presence of P...
متن کامل