Relationship between the octanol-water partition coefficient of tertiary amines and their effect of ‘selective’ uncoupling of photophosphorylation |
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Authors: | Henrik Laasch |
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Institution: | (1) Institut für ökologische Pflanzenphysiologie und Geobotanik, Heinrich-Heine-Universität Düsseldorf, Universitätsstrasse 1, D-4000 Düsseldorf, Federal Republic of Germany |
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Abstract: | A series of tertiary amines was investigated for effects on the transmembrane proton potential difference (
H), on photophosphorylation and on electron-flux control related to the intrathylakoid proton potential (
HI), using isolated chloroplasts ofSpinacia oleracea L. As indicated by 9-aminoacridine fluorescence and 14C]methylamine uptake, all amines studied inhibited a build-up of
H and, in parallel, ATP synthesis. Even when
H was low, strong
H1-dependent electron-flux control was observed under the influence of tertiary amines. The strength of flux control in the presence of low
H and the effectiveness of inhibition of ATP synthesis linearly increased with the lipophilicity of the amines. The most effective of the amines tested caused 50% inhibition of ATP synthesis at a concentration of 6 M, which is about 1000-fold lower than the concentration required for inhibition by methylamine. The data presented indicate the existence of two proton domains in the thylakoid vesicles, one of them feeding the ATP-synthase, the other the sites of pH-dependent electron-flux control. It is concluded that tertiary amines develop their action in a lipophilic domain of the thylakoid membrane, in the vicinity of the ATP-synthase complex. A mechanism for selective uncoupling and for the maintenance of
HI-dependent electron flux control in the presence of low
H is discussed.Abbreviations and symbols
coefficient for pH-dependent electron flux control
- 9-AA
9-aminoacridine
- Chl
chlorophyll
- I50
amine concentration producing 50% inhibition of ATP-synthesis
- Je
flux of photosynthetic electron transport
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k
H
apparent rate constant for proton efflux
-
H1
proton potential in the thylakoid lumen
-
H1
transthylakoid proton potential difference
-
p
partition coefficient
-
q
AA
coefficient for 9-aminoacridine fluorescence quenching
- PS
photosystem
- Q
quantum flux of photosynthetically active light
Dedicated to Professor Wilhelm Simonis, on the occasion of his 80th birthday |
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Keywords: | Amine tertiary Photophosphorylation (selective uncoupler) Photosynthetic electron transport Spinacia (photosynthesis) Tertiary amine |
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