Summary
InNitella cells with low pump activity, the electrical characteristics of membrane transport are mainly determined by K+ transport. Current-voltage curves were measured at outside K+ concentrations ranging from 0.1 to 100 mol m−3. Above 1 mol m−3, current saturated at positive and at very negative potentials. It was found that theseI–V curves could be fitted by a Class 1, case 1 reaction kinetic model, which is a cyclic reaction scheme with one pair of rate constants sensitive to membrane potential (Class I) and neutral transporter (or electrically charged substrate-transporter complex, case I). The analysis revealed the relative rate constants of a 3-state model. From the linear dependence of the rate constant of substrate binding (k 32) on [K+] a′ the stoichiometry of 1 K+/cycle was obtained. The complex transporter substrate is very unstable (very high value ofK 23) resulting in a very low density of this state and in what can be called Mitchellian behavior; namely, the driving forces resulting from the electrical and from the concentration gradient can hardly be distinguished.
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Fisahn, J., Hansen, UP. & Gradmann, D. Determination of charge, stoichiometry and reaction constants fromI–V curve studies on a K+ transporter inNitella . J. Membrain Biol. 94, 245–252 (1986). https://doi.org/10.1007/BF01869720
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DOI: https://doi.org/10.1007/BF01869720