The role of potassium in charge compensation for sucrose-proton-symport by cotyledons of Ricinus communis [castor-oil plant]
1980
Cho, B.H. | Komor, E. (Regensburg Univ. (Germany, F.R.). Fachbereich Biologie und Vorklinische Medizin)
The addition of sucrose to cotyledons of Ricinus communis caused a transient uptake of protons and, simultaneously, a transient efflux of potassium ions. The stoichiometry was up to approx. 0.3. protons taken up per sucrose and up to 0.6. potassium ions released per sucrose. The presence of lipophilic cations or anions strongly reduced the potassium efflux with less change of the proton/sucrose stoichiometry. It is concluded that the uptake of protons with sucrose is mechanistically coupled by the sucrose transport system whereas the potassium efflux occurs passively by some other path and is caused by membrane potential depolarisation. The sucrose uptake system is therefore an electrogenic proton symport system, and the efflux of potassium only serves for charge compensation.
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