Abstract
A series of tertiary amines was investigated for effects on the transmembrane proton potential difference (Δ \(\tilde \mu \)H), on photophosphorylation and on electron-flux control related to the intrathylakoid proton potential (\(\tilde \mu \)HI), using isolated chloroplasts ofSpinacia oleracea L. As indicated by 9-aminoacridine fluorescence and [14C]methylamine uptake, all amines studied inhibited a build-up ofΔ \(\tilde \mu \)H and, in parallel, ATP synthesis. Even whenΔ \(\tilde \mu \)H was low, strong\(\tilde \mu \)H1-dependent electron-flux control was observed under the influence of tertiary amines. The strength of flux control in the presence of lowΔ \(\tilde \mu \)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 μM, 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\(\tilde \mu \)HI-dependent electron flux control in the presence of lowΔ \(\tilde \mu \)H is discussed.
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Abbreviations
- α:
-
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
- k H :
-
apparent rate constant for proton efflux
- \(\tilde \mu \)H1 :
-
proton potential in the thylakoid lumen
- Δ\(\tilde \mu \)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
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Dedicated to Professor Wilhelm Simonis, on the occasion of his 80th birthday
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Laasch, H. Relationship between the octanol-water partition coefficient of tertiary amines and their effect of ‘selective’ uncoupling of photophosphorylation. Planta 178, 553–560 (1989). https://doi.org/10.1007/BF00963826
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DOI: https://doi.org/10.1007/BF00963826