Summary
H+-coupled transport in plant and fungal cells is relatively insensitive to external pH (pH o ). H+-coupled Cl− transport at the plasma membrane ofChara corallina was studied to explore the phenomena responsible for this insensitivity. Raising pH o from a control value of 7.5 to 9.0 results in a modest (2.5-fold) decline inJ max and increase inK m . Further increase in pH o results in a selective increase inJ max, in accordance with predictions from a reaction kinetic model of the transport system (Sanders, D., Hansen, U.-P., 1981.J. Membrane Biol. 58:139–153). Increase in cytosolic Cl− concentration ([Cl−] c ) also results in a selective decrease inJ max at pH o =7.5.
Quantitative kinetic modeling of the results is not possible if it is assumed that the sole effect of pH o isvia mass action on the binding of external H+ to a transport site. If, instead, the dependence of cytosolic pH (pH c ) on pH o (Smith, F.A., 1984,J. Exp. Bot. 35:1525–1536) is taken into account along with the dependence of Cl− influx on pH c (Sanders, D., 1980,J. Membrane Biol. 53:129–141), then the observed modest changes in Michaelis parameters can be accommodated by a reaction kinetic model. The quantitative parameters of the model yield respective pK a s of the internal and external H+-binding sites=7.85 and 7.2, respective dissociation constants of the internal and external Cl−-binding sites=160 and 40 μm, and an additional, kinetically transparent, H+-binding site with a pK a >8.0. The quantitative model independently predicts the response ofJ max andK m to acidic conditions.
The results are discussed in terms of the general physiological requirement that fluxes through H+-coupled transport systems are relatively insensitive to environmental variation in pH o . It is proposed that (i) the weak (but finite) dependence of pH c on pH o , coupled with (ii) the strong dependence of H+-coupled transport on pH c are instrumental in endowing H+-coupled transport systems with a relative insensitivity to variation in pH o . This hypothesis might also explain why pH c in plants and fungi is not acutely controlled with respect to variation of pH o .
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References
Ballarin-Denti, A., Hollander, J.A. den, Sanders, D., Slayman, C.W., Slayman, C.L. 1984. Kinetics and pH-dependence of glycine-proton symport inSaccharomyces cerevisiae.Biochim. Biophys. Acta 778:1–16
Beilby, M.J. 1981. Excitation-revealed changes in cytoplasmic Cl− concentration in “Cl−-starved” cells.J. Membrane Biol. 62:207–218
Beilby, M.J., Walker, N.A. 1981. Chloride transport inChara. I. Kinetics and current-voltage curves for a probable proton symport.J. Exp. Bot. 32:43–54
Eddy, A.A. 1982. Mechanisms of solute transport in selected eukaryotic microorganisms.Adv. Microb. Physiol. 23:1–78
Felle, H. 1981. Stereospecificity and electrogenicity of amino acid transport inRiccia fluitans.Planta 152:505–512
Hutchings, V.M. 1978. Sucrose and proton cotransport inRicinus cotyledons I. H+ influx associated with sucrose uptake.Planta 138:229–235
Hutchinson, G.E. 1975. A Treatise on Limnology. Vol. III. Limnological Botany. Wiley, New York
Jayasuria, H.D. 1975. Ion Transport in Characean Cells. Ph.D. Thesis. University of Cambridge, Cambridge
Komor, E., Schwab, W.G.W., Tanner, W. 1979. The effect of intracellular pH on the rate of hexose uptake inChlorella.Biochim. Biophys. Acta 555:524–530
Komor, E., Tanner, W. 1974. The hexose-proton cotransport system ofChlorella. pH-dependent change inK m values and translocation constants of the uptake system.J. Gen. Physiol. 64:568–581
Lass, B., Ullrich-Eberius, C.I. 1984. Evidence for proton/sulfate cotransport and its kinetics inLemna gibba G1.Planta 161:53–60
Lucas, W.J., Keifer, D.W., Pesacreta, T.C. 1986. Influence of culture medium pH on charasome development and chloride transport inChara corallina.Protoplasma 130:5–11
Marquardt, D.W. 1963. An algorithm for least squares estimation of non-linear parameters.J. Soc. Indust. Appl. Math. 11:431–441
Novacky, A., Fischer, E., Ullrich-Eberius, C.I., Lüttge, U., Ullrich, W.R. 1978. Membrane potential changes during transport of glycine as a neutral amino acid and nitrate inLemna gibba G1.FEBS Lett. 88:264–267
Reid, R., Walker, N.A. 1984. Control of Cl− influx inChara by internal pH.J. Membrane Biol. 78:157–162
Rodriguez-Navarro, A., Blatt, M.R., Slayman, C.L. 1986. A potassium-proton symport inNeurospora crassa.J. Gen. Physiol. 87:649–674
Sanders, D. 1980a. Control of Cl− influx inChara by cytoplasmic Cl− concentration.J. Membrane Biol. 52:51–60
Sanders, D. 1980b. Control of plasma membrane Cl− fluxes inChara corallina by external Cl− and light.J. Exp. Bot. 31:105–118
Sanders, D. 1980c. The mechanism of Cl− transport at the plasma membrane ofChara corallina: I. Cotransport with H+.J. Membrane Biol. 53:129–141
Sanders, D. 1984. Gradient-coupled chloride transport in plant cells.In: Chloride Transport Coupling in Cells and Epithelia. G.A. Gerencser, editor. pp. 63–120. Elsevier/North-Holland, Amsterdam
Sanders, D., Hansen, U.-P. 1981. Mechanism of Cl− transport at the plasma membrane ofChara corallina: II. Transinhibition and the determination of H+/Cl− binding order from a reaction kinetic model.J. Membrane Biol. 58:139–153
Sanders, D., Hansen, U.-P., Gradmann, D., Slayman, C.L. 1984. Generalized kinetic analysis of ion-driven cotransport systems: A unified interpretation of selective ionic effects on Michaelis parameters.J. Membrane Biol. 77:123–152
Sanders, D., Slayman, C.L. 1982. Control of intracellular pH. Predominant role of oxidative metabolism, not proton transport, in the eukaryotic microorganismNeurospora.J. Gen. Physiol. 80:377–402
Sanders, D., Slayman, C.L., Pall, M.L. 1983. Stoichiometry of H+/amino acid cotransport inNeurospora crassa revealed by current-voltage analysis.Biochim. Biophys. Acta 735:67–76
Sanders, D., Smith, F.A., Walker, N.A. 1985. Proton/chloride cotransport inChara: Mechanism of enhanced influx after rapid external acidification.Planta 163:411–418
Schwab, W.G.W., Komor, E. 1978. A possible mechanistic role of the membrane potential in proton-sugar cotransport ofChlorella.FEBS Lett. 87:157–160
Slayman, C.L., Slayman, C.W. 1974. Depolarization of the plasma membrane ofNeurospora during active transport of glucose: Evidence for a proton-dependent cotransport system.Proc. Natl. Acad. Sci. USA 71:1935–1939
Smith, F.A. 1984a. Regulation of the cytoplasmic pH ofChara corallina: Response to changes in external pH.J. Exp. Bot. 35:43–50
Smith, F.A. 1984b. Regulation of the cytoplasmic pH ofChara corallina in the absence of external Ca2+: Its significance in relation to the activity and control of the H+ pump.J. Exp. Bot. 35:1525–1536
Smith, F.A., MacRobbie, E.A.C. 1981. Comparison of cytoplasmic pH and Cl− influx in cells ofChara corallina following “Cl− starvation.”J. Exp. Bot. 32:827–835
Smith, F.A., Raven, J.A. 1979. Intracellular pH and its regulation.Annu. Rev. Plant Physiol. 30:289–311
Smith, F.A., Walker, N.A. 1976. Chloride transport inChara corallina and the electrochemical potential difference for hydrogen ions.J. Exp. Bot. 27:451–459
Ullrich, W.R., Novacky, A. 1981. Nitrate-dependent membrane potential changes and their induction inLemna gibba G1.Plant Sci. Lett. 22:211–217
Ullrich-Eberius, C.I., Novacky, A., Bel, A.J.E. van. 1984. Phosphate uptake inLemna gibba G1: Energetics and kinetics.Planta 161:46–52
Ullrich-Eberius, C.I., Novacky, A., Fischer, E., Lüttge, U. 1981. Relationship between energy-dependent phosphate uptake and the electrical membrane potential inLemna gibba G1.Plant Physiol. 67:797–801
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Sanders, D., Hopgood, M. & Jennings, I.R. Kinetic response of H+-coupled transport to extracellular pH: Critical role of cytosolic pH as a regulator. J. Membrain Biol. 108, 253–261 (1989). https://doi.org/10.1007/BF01871740
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DOI: https://doi.org/10.1007/BF01871740